问题 选择题

下列关于声现象说法中正确的是  [ ]

A.只要振动,人们就能听到声音

B.在真空中听不到声音,是因为声音只能在空气中传播

C.声音在水中比在空气中传播得慢

D.小提琴的声音悦耳动听给人们以享受,但有时也会成为噪音

答案

答案:D

阅读理解

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There's an old saying, “You can put more salt in the soup,but once it's in there,you can't get it out.”__1__ And your child can help!Here's an exciting experiment for your child to try:

Start by helping your child to mix salt into the water in the mixing bowl and stirring until it is fully dissolved溶解).

___2__ Make sure that you don't let any of the salty water into it.

___3__ Then take a small rock,and place it right on top of the center of the plastic wrap,so that all of the plastic leans slightly toward the middle of the bowl where the cup is.

Put the whole setup in full,hot sun,and wait. Within an hour, you should see water droplets begin to form on the underside of the plastic. __4___

Wait, and then take the plastic off. A good amount of water should be in the small cup.

__5__ Guess what? No salt!The water vaporized蒸发)in the heat of the sun,and then returned to its liquid state. Salt doesn't do that一it stayed behind. You really can take the salt out of salt water!

As it happens,this is an excellent lesson in the way matter can change states.

A.Fresh water is scarcer than ever.

B.Invite your child to taste with you.

C.Water can go from liquid to gas and to liquid again.

D.Cover the bowl with plastic wrap and seal the edges.E.Then place a cup or a smaller bowl into the center of the bowl.

F.They'll flow and drip into the center of the bowl,and into the cup.

G..Today, scientists are busy exploring ways to take the salt out of salt water in large quantities.

单项选择题