Deserts are found where there is little rainfall or where rain for a whole year falls in only a few weeks' time. Ten inches of rain may be enough for many plants to survive (存活) if the rain is spread throughout the year, If it falls within one or two months and the rest of the year is dry, those plants may die and a desert may form.

    Sand begins as tiny pieces of rock that get smaller and smaller as wind and weather wear them down. Sand dunes (沙丘) are formed as winds move the sand across the desert. Bit by bit, the dunes grow over the years, always moving with the winds and changing the shape. Most of them are only a few feet tall, but they can grow to be several hundred feet high.

    There is, however, much more to a desert than sand. In the deserts of the southwestern United States, cliffs (悬崖) and deep valleys were formed from thick mud that once lay beneath (在……之下) a sea more than millions of years ago. Over the centuries, the water dried up. Wind, sand, rain, heat and cold all wore away at the remaining rocks. The faces of the desert mountains are always changing--very, very slowly--as these forces of nature continue to work on the rock.

    Most deserts have a surprising variety of life. There are plants, animals and insects that have adapted (适应) to life in the desert. During the heat of the day a visitor may see very few signs of living things, but as the air begins to cool in the evening, the desert comes to life. As the sun begins to rise again in the sky, the desert once again becomes quiet and lonely.

There are a few ways to test how smart animals are. {#blank#}1{#/blank#} method is to test memory. Scientists in Japan {#blank#}2{#/blank#} a group of college students and a group of five-year-old chimps the numbers one to nine in different places on a computer screen. The test was to see {#blank#}3{#/blank#} the groups could remember the position of the numbers in the correct order. Each time the chimps were {#blank#}4{#/blank#} than the students. Why? Were the chimps special in a way? Did someone assist them? No, but the chimps probably had an important {#blank#}5{#/blank#} They were young. As both humans and animals get older, their memory gets worse.

Have you ever kept putting your head down to look at a screen until your neck hurts？1 so，you've experienced tech neck.Tech neck takes place when the use of phones，computers and other technology causes neck pain.These days it's a common problem2 .

Your neck muscles（肌肉） are designed to hold your3 upright（竖直的）.They can also move your head around.But bending（弯曲） your head forward4 a long time can pull your muscles hard.That can make them5 .

In the past people spent most of their time looking up.But now people spend more time looking6 at their phones.They often hold them far below the head.This causes people to have to crane（伸长） their necks to see the phone7 which，in turn，causes tech neck.Bending over to watch the screen of a computer on a desk can have a similar8 .

It might be impossible to expect people to give up their phones to 9 tech neck.And completely refusing technology isn't necessary.However，you can do10 to improve this situation.

First，you can hold your phone up higher——so you don't have to bend down to look at it.But this can be tiring for your either11 .So keep your head upright，and look only with your eyes.When using the computer，try to12 straight as well.Slumping in front of a screen can hurt your back.

Also，take13 .Once in a while，look up from your screen，and move your shoulders back.If you've been sitting14 at times to relax your muscles.

If you continue experiencing tech neck，you can do exercises to feel good.Tech neck is a 15 result of using today's technology，but it doesn't have to be.If you are serious about the problem，you can take actions to avoid it.

Travel and tourism(旅游) are very important to millions of people all over the world. It's important to some countries too. They need the money from tourism to help their people live better. 

However, travel and tourism cause many problems. Planes, buses, boats and other ways of transportation that carry travellers and tourists cause pollution. Moreover, some people do things on holiday that they would never think of doing at home. For example, many travellers use a lot of water and electricity when they stay in hotels. They forget to turn off the lights or even leave televisions and air-conditions on when they leave the room. That's why it is important for people to travel wisely and respect(尊重) the places they visit. 

There are ways you can travel and be environmentally friendly. Here are some tips to help you. 

●Don't throw rubbish anywhere. Use bins(垃圾桶). Don't throw anything into the sea, especially plastic bags. Every year many sea animals die because of plastic bags. 

●Don't waste water or electricity. Many parts of the world have not got enough water. 

●Don't buy any products made from endangered animals.