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 (结冰) 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. 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(任务) 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
