Look up in the sky. Do you see any clouds? What do they look like? Some clouds are fluffy(绒毛状的) and white, like cotton balls. Others are dark almost black, and make you hold an umbrella. At sunrise and sunset, clouds can look red, purple, or yellow—as if they were colored with crayons. But what are clouds anyway?

    You can't reach out and touch the clouds, but you can make your own in a bottle.

    You need

    * an adult helper

    * a huge, empty glass jar

    * a metal strainer(过滤器)

    * hot water

    * ice

    Do these

    Step1. Have your helper fill the jar with hot water, leave it there for two minutes, then pour out most of the water. Leaving just an inch or two at the bottom of the jar.

    Step2. It's your turn, put the strainer over the mouth of the jar, fill the strainer with ice. Watch the jar.

    What happened?

    A cloud formed in the jar! Some of the hot water at the bottom of the jar turned into hot water vapor(蒸汽). The water vapor rose and met with the cold air coming off the ice. When the water vapor condensed, it formed a cloud. Hot air rises and carries with it lots of water vapor, the higher the air rises, the more it cools down. Soon the cold air can't hold all the water vapor so it starts turning into tiny water drops, and becomes a cloud.

    The tiger is the largest wild cat in the world. It is the king of animals. Tigers often eat 5kg of meat for a meal. Tigers can see very well in the dark. They often hunt at night. Sometimes they can eat 27kg of meat at one night. Most members of the cat family dislike water, but tigers enjoy water. They are good at swimming. Many animals live in groups, but tigers live alone（单独地）, except for（除了） mothers and their young babies. A mother tiger usually has two or three babies at one time. She takes care of them by herself.

    There were eight kinds of tigers in the world, but three of them died out（灭绝）. There are only about 3200wild tigers in the world now because people kill tigers and destroy the places where they live.

    Everybody hates rats. But rats may soon be man's new good friends. What happens after an earthquake? We send in rescue dogs. Why? Because they can smell people. Dogs save lives. They help rescuers to find living people. But dogs are big and they can't get into small spaces. So now a new research project is using a smaller animal to save lives: the rat.

    How does it work? First, the rat is trained to smell people. When this happens, the rat's brain gives a signal. This is sent to a small radio on its back, and then the rescuers follow the radio signals. When the rat's brain activity jumps, the rescuers know that someone is alive. The rat has smelled that person.

    Although there are already robots which can do this job, rats are better. Robots' noses don't work well when there are other smells around. Rats are good at that. Rats can also see in the dark, they are cheaper and quicker to train than dogs, and unlike robots, they don't need electricity!

    The "rat project" is not finished. But a scientist says, "It would be great. A rat could get into any place we couldn't get to, and a rat would get out if it wasn't safe." Perhaps for the first time in history, people will be happy to see a rat in a building (but only after an earthquake, of course).

Information Card

House fires cause many deaths each year and a large number of these fires are unfortunately set by children.{#blank#}1{#/blank#}Kids must understand that they'd better not play with fire. You should keep matches and lighters out of their reach.

{#blank#}2{#/blank#} The main job of such an alarm is to protect you while you're asleep. You should have a smoke alarm outside each bedroom and on each floor of your home. You ought to have two plans for getting out of your house if there is a fire and practise these plans in the dark with your family.

A smoke alarm warns you of the danger. {#blank#}3{#/blank#}Take action immediately. When you come to a closed door, check it with the back of your hand. If it feels hot, there may be smoke or fire behind the door, so take care. Once you are out of your house, call the fire department from a neighbor's house. If a family member or a pet is caught inside, you shouldn't go back in. Firemen know how to perform rescues safely.

{#blank#}4{#/blank#} Change the batteries at least once a year. You should use the test button each month to see if the alarm and batteries are still working. A smoke alarm lasts about ten years. You ought to change it even if it seems to be working.