问题补充：
It is easier to float in the ocean than it is to float in a swimming pool. Do you know why?
Ocean water is full of salt— and salt water can hold up more weigh than fresh water. See for yourself!
You Will Need:
● 3 cups of warm water
● Measuring cup (量杯)
● Wide-mouthed jar
● Salt
● Spoon
● Raw (生的)potato
You Will Do:
1. Pour 1.5 cups of warm water into the jar.
2. Add 1/3 cup of salt.
3. Stir(搅拌) until the salt is completely dissolved.
4. Add another 1.5 cups of water. Pour it slowly over the back of the spoon into the jar so that the two liquid will not mix together.
5. Gently place the potato into the jar. Do not drop it.
What Will Happen:
The potato will sink— but only halfway!
Why?
Salt water is heavier than fresh water, so it will stay on the bottom. The fresh water will remain on top.
The potato is heavier than the fresh water, but it is lighter than the salt water. That is why the potato will sink halfway down.
【小题1】In the experiment, what should you do right after you pour the water over the spoon?【小题2】In Step 4 of the experiment, why do you pour the water over the spoon “slowly”?【小题3】In which step of the experiment do you add the salt?【小题4】What does the underlined word “gently” mean?
A. Carefully
B. Quickly
C. Secretly
D. Silently
答案：
A. Carefully
B. Quickly
C. Secretly
D. Silently
解析：本文介绍了一个证明盐水的浮力比淡水的浮力大的实验。
【小题1】C 细节题。根据You Will Do:中的5 Gently place the potato into the jar. Do not drop it说明C正确。
【小题2】D 细节题。根据Add another 1.5 cups of water. Pour it slowly over the back of the spoon into the jar so that the two liquid will not mix together中的so that the two liquid will not mix together指这两种液体不要混在一起。故D正确。
【小题3】B 细节题。根据You Will Do:中的2 Add 1/3 cup of salt.说明B正确。
【小题4】A 推理题。根据Gently place the potato into the jar. Do not drop it中的Do not drop it不要扔下去，说明要轻轻地放，故A正确。
