you must not touch the ice with your fingers （手指）.

　　You may ask your friends to try to do that when you are having dinner together. There is a saltcellar on the table. You must use salt when you carry out this experiment.

　　First you put the string across the piece of ice. Then put some salt on the ice. Salt makes ice melt(融化). The ice round the string will begin to melt. But when it melts, it will lose heat. The cold ice cube will make the salt water freeze（冻结） again.

　　After a minute or two you may raise（提起） the piece of string and with it you will raise your piece of ice!

　　This experiment can be very useful to you. If, for example, there is ice near the door of your house, you must use very much salt to melt all the ice. If you don't put enough salt, the water will freeze again.

8．We must use _______ when we do this experiment.

A. fridge B. some food C .a table D. some salt

9．How long will it take to do this experiment?

A. More than three minutes. B. Five minutes or so.

C. Only one minute or two. D. About ten minutes.

10．What is the task of this experiment?

A. Put the ice cube into the glass of water with the help of the string.

B. Take out the ice cube in the glass of water with the help of the string.

C. Take out the ice cube in the glass of water with your fingers.

D. Put some salt on the ice cube and then put the string across it.

11．How many things at least(至少） are used in this experiment?

A. Three. B. Four. C.Six. D. Seven.

Stephen Hawking is one of the most famous scientists in this century. He was born in 1942. He's world well-known on space and time. Stephen was searching some very big questions, such as "How did the universe begin? How will it end?"

Stephen was a student at Oxford University. He studied math and science. Then, at the age of twenty, he became sick. He was so young, but the doctors said to his family, "He has only two more years to live." As a matter of fact, the doctors were wrong - he didn't die. He can't walk but he uses a wheelchair. He can't feed himself and get in or out of bed himself. But he refused to give in to the condition. He talks with the help of a computer. After Oxford, Stephen went to Cambridge University. Three years later, in 1965, he became a doctor of philosophy(哲学).