If you can find a tree which has been cut down，you will see many rings，or circles，on the base of the trunk.By learning to read these rings，you can find out about the tree's life.

    The number of rings tells you how old the tree is.Each year，new wood is formed on the outside of the tree.This new wood is light in color when the tree is growing in spring and summer，and dark in winter when the tree is not growing much.So，if you count the rings of dark­or­light colored wood，you can often find out how old the tree is.

    You can also tell which years have been good years and which years have been bad years.When the light­colored rings are very wide，it means that the tree has been growing quickly that year.If the rings are narrow，it has been growing slowly.If the rings on a tree trunk were greatly magnified，you would be able to see why the rings are light­colored when the tree is growing quickly and dark­colored when the tree is growing slowly.The tree trunk is made up of microscopic tubes，like some pipes，carrying water from the soil，through the trunk，and up to the leaves.They are wide and thin­walled when the tree is growing quickly and they are carrying a lot of water.They are narrow and stuck together when the tree is not growing so quickly.

    When a tree is old，the tubes in the centre of the tree don't carry water.The walls of the tubes have become thick with materials which have stuck along them over the years，forming a kind of wood called“heartwood”．This kind of wood is darker in color than the young，growing wood on the outside of the tree.

    You don't very often see whole tree trunks which have been cut across.But once you learn to read a cross section of the wood，you can see much more in wood which has been used to make boxes，houses and other things.

    In most wood，instead of seeing the trunk cut across，you are seeing it cut along its length.Because you don't see the whole tree，you can't tell how old it is.

Title：{#blank#}1{#/blank#} of a Tree

New York City Tour Guide

CENTRAL PARK PHOTO TOUR $79

With Sam L.

    Come to shoot in the Central Park of New York that will allow you to take home digital postcards.This tour is a great introduction to Central Park and combines views of the bridges,lakes and skyline.

    At each stop of the photo tour,I will provide you with explanations around photography（摄影）,camera settings, etc.You will be able to put these tips to good use immediately.

NEW YORK RUNMNG TOUR $50

With Sebastien B.

    Love running?Love New York?Do you want to see the sites of the city?Contact me and we'll take a special tour. All you'll need to do is to put on your sports shoes and we'll be off.I'll show you my favorite running spots along the Hudson River or north of Central Park and away from all the tourists.

    If you're thinking of training for something,I'll give you the explanations and tips to make the best of your time training!

GREENWICH VILLAGE FOOD TOUR $75

With Manhattan W.

    Discover unbelievable places to eat.This is the real Greenwich Village gastronomic（美食的）experience.Along the way,find out how the village has kept its unique character throughout the years,from the Dutch and English controlled periods to today.

Tour runs every day from 12:30 PM-2:30 PM.

NEW YORK BY NIGHT PHOTO TOUR $115

With Sam L.

    We have already prepared NYC for the most unique points for you.During the  hour walking tour,we share these special comers of NYC.

    The night tour teaches night photography techniques while discovering the "darker" side of the city that never sleeps: the UN headquarters,42nd street,Grand Central Terminal,the Chrysler Building,Rockefeller Center and Radio City Music Hall.

    A black hole is created when a large star burns out. Like our sun, stars are unbelievably hot furnaces(熔炉) that burn their own matter as fuel. When most of the fuel is used up, the star begins to die.

    The death of a star is not a quiet event. First there is a huge explosion. As its outer layer is blasted off into space, the dying star shines as brightly as a billion suns.

    After the explosion, gravity pulls in what's left of the star. As the outside of the star sinks toward the center, the star gets smaller and smaller. The material the star is made of becomes tightly packed together. A star is so solid that a teaspoon of matter from it weighs billion of pounds.

    The more the star shrinks(收缩), the stronger the gravity inside it becomes. Soon the star is very tiny, and the gravity pulling it in is unbelievably strong. In fact, the gravity is so strong that it even pulls light into the star! Since all the light is pulled in, none can go out. The star becomes black when there is no light. Then a black hole is born!

    That's what we know about black holes. What we don't know is this: What happens inside a black hole after the star has been squeezed into a tiny ball? Does it keep getting smaller and smaller forever? Such a possibility is hard to imagine.

    But if the black hole doesn't keep shrinking, what happens to it? Some scientists think black holes are like doorways to another world. They say that as the star disappears from our universe, it goes into another universe. In other words a black hole in our universe could turn into a "white hole" in a different universe. As the black hole swallows(吞噬) light, the white hole shines brightly--somewhere else. But where? A different place, perhaps, or a different time--many years in the past or future.

    Could you travel through a black hole? Right now, no. Nothing we know of could go into a black hole without being crushed(挤压). So far the time being, black hole must remain a mystery.

    Black holes are a mystery--but that hasn't stopped scientists from dreaming about them. One scientist suggested that in the future we might make use of the power of black holes. They would supply all of Earth's energy needs, with plenty to spare. Another scientist wondered if a black hole could some day be used to swallow earthly waste--a sort of huge waste disposal(处理) in the sky!

How to Meet New People

    It is easy to find a place where people gather. But once you're in a room full of people, then what? The trick is finding a way to approach someone and get them talking to you.

    Prepare to meet new people before you arrive. {#blank#}1{#/blank#}. Don't think in terms of yes or no questions. You should consider questions that will allow the person to contribute more than a one-word answer to the conversation.

    Arrive at your event or place. Don't panic when you walk in the door. Take your time and look over the room. If this is a classroom, take a seat and look around the room. {#blank#}2{#/blank#}, take time to enjoy the art while looking at the people. Don't rush into talking to someone. You have time, so just get a feel for the group.

    Approach someone. {#blank#}3{#/blank#}. But remember, if the person is at the event alone, they may also be shy and try to break out and meet people. You need to make them feel comfortable by chatting with them.

    {#blank#}4{#/blank#}. Keep them talking and talk yourself—remember  conversation goes in two directions. You may have a couple of awkward moments, but if you have a few items planned to talk about, you'll find that they'll start adding their own questions and information to the conversation.

    Don't forget to ask them for a friendship follow-up. {#blank#}5{#/blank#}, try asking your new friend if they'd like to go to another event with you. If it is a repeat event, such as a class, try asking them if they'd like to meet for coffee before the next class to study the material.

A. If it is a one-time event

B. If this is an art show

C. If you have picked out someone to approach

D. Mentally pull out your prepared questions

E. You may not meet your next best friend on your first try

F. You might find it easiest to approach someone who is also alone

G. Sit down and write out a list of potential questions you can ask someone

    The common cold is the world's most widespread illness, which is probably why there are more myths(神话) about it than any of the other illnesses.

    The most widespread mistake of all is that colds are caused by cold. They are not. They are caused by viruses passing on from person to person. You catch a cold by coming into contact, directly or indirectly, with someone who already has one. If cold causes colds, it would be reasonable to expect the Eskimos to suffer from them forever. But they do not. And in isolated Arctic regions explorers have reported being free from colds until coming into contact again with infected(感染的) people from the outside world by way of packages and mails dropped from airplanes.

    At the Common Cold Research Unit in England, volunteers took part in Experiments in which they gave themselves to the discomforts of being cold and wet for long stretches of time. After taking hot baths, they put on bathing suits, allowed themselves to be doused(浸入) with cold water, and then stood about dripping(滴干)wet in drafty(通风的) rooms. Some wore wet socks all day while others exercised in the rain until close to exhaustion. Not one of the volunteers came down with a cold unless a cold virus was actually dropped in his nose.

    If cold and wet have nothing to do with catching colds, why are they more frequent in the winter? In spite of the most painstaking research, no one has yet found the answer. One explanation offered by scientists is that people tend to stay together indoors more in cold weather than at other times, and this makes it easier for cold viruses to be passed on.

    No one has yet found a cure for the cold. There are drugs and pain suppressors such as aspirin, but all they do is to relieve the symptoms.

Pick up any packaged processed food, and there's a decent chance that one of its listed ingredients will be "natural flavour". The ingredient sounds good, particularly in contrast to "artificial flavours" since there is a common belief that ingredients from nature are necessarily safer than something artificially made. But it's not true. Then what exactly does the natural flavour mean? It refers to extracts (提取物) got from natural sources like plants, meat or seafood. When consumers see the "natural flavour" on a label, they are unlikely to assume that someone is squeezing the juice from oranges into their bottles. They know even though natural flavour must come from natural sources, it needn't all come from the plant or meat. For example, orange flavours might contain not only orange extracts, but also extracts from bark and grass.

So if flavours like orange are needed, why not just use oranges? The answer comes down to "availability, cost, and sustainability", according to flavour chemist Gary Reineccius of the University of Minnesota. "If you're going to use all your grapes on grape soda," Reineccius says, "you don't have any grapes for wine making; the products are going to be exorbitant; besides, what do you do with the by-products you create after you've squeezed all the juice out of the grapes?"

Actually, while chemists make natural flavours by extracting chemicals from natural ingredients, artificial flavours are made by creating the same chemicals artificially. The reason why companies bother to use natural flavours rather than artificial flavours is simple: marketing. "Many of these products have health titles," says Platkin, professor from Hunter College. "Consumers may be talked to believe products with natural flavours are healthier, though they are nutritionally no different from those with artificial flavours. Natural flavours may involve more forest clear-cutting and carbon emissions from transport than flavours created in the lab."

Platkin suggests getting more transparent (易懂的) labeling on packaging that describes exactly what the natural or artificial flavours are, so consumers are-not misled into buying one product over another because of "natural flavours". Reineccius also offers simple guidance: "Don't buy anything because it says ‘natural flavours'. Buy it because you like it."