Put an ice cube from your fridge into a glass of water. You have a piece of string(线) 10 centimeters long. The problem is to take out that piece of ice with the help of the string. But you must not touch the ice with your fingers.

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 again. After a minute or two you may raise 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.

1. We must use _______ when we carry out this experiment.

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

2. How long will it take to carry out this experiment?

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

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

3. 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.

4. How many things at least are used in this experiment?

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

5. We can learn something about _______ from the passage.

A. physics    B. biology   C. chemistry   D. maths

 

 0  42147  42155  42161  42165  42171  42173  42177  42183  42185  42191  42197  42201  42203  42207  42213  42215  42221  42225  42227  42231  42233  42237  42239  42241  42242  42243  42245  42246  42247  42249  42251  42255  42257  42261  42263  42267  42273  42275  42281  42285  42287  42291  42297  42303  42305  42311  42315  42317  42323  42327  42333  42341  151629 

违法和不良信息举报电话:027-86699610 举报邮箱:58377363@163.com

精英家教网