22、

1．A thermometer is used in the experiment for       .

      A．marking              B．measuring            C．freezing               D．timing

2．When should the timing begin?

       A．Before you label the plain water.            B．After you finish stirring the salt water

       C．When ice starts to form on water.         D．As soon as both cups are in a freezer

3．By doing this experiment, the writer intends to       .

       A．record the exact freezing point at which salt water turns frozen

       B．draw a conclusion that fresh and salt water freeze at the same time

       C．prove a guess that salt water is different from fresh water in freezing

       D．a(chǎn)ffect the time and temperature at which salt water freezes