1. 阅读下列短文，从下面每小题的A.B.C .D四个选项中选出最佳选项。

    It is easier to float in the ocean than in a swimming pool. Do you know why?

    Ocean water is full of salt - and salt water can hold up more weight than fresh water. See for yourself! (Ask an adult to help you.)  You will need: 3 cups warm water; A wide-mouth jar（罐）; Salt; A spoon; A 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(完全溶解) 4. Add another l.5 cups of water. Pour it slowly over the back of the spoon into the jar so that the two kinds of water will not mix together. 5. Softly place the potato into the jar. Don't 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 the top. The potato is heavier than the fresh water, but it is lighter than the salt water. That is why the potato will sink only halfway down.

1. （1） What don't we need for the experiment?    

   A . Some water. B . Some juice. C . Some salt. D . A potato.
3. （2） In the experiment, what should we do right after we first pour l.5 cups of warm water into the jar?

   A . Add the salt to the water. B . Stir the water quickly. C . Put the potato into the jar. D . Add some more warm water into the jar.
5. （3） Why do we pour the water over the back of the spoon slowly?

   A . It is easier to see what you are doing.     B . It keeps the water from running out.     C . It pushes the fresh water to the bottom. D . It will keep the two kinds of water from mixing together.
7. （4） Which of the following is TRUE according to the passage?    

   A . Salt water can't hold up more weight than fresh water.    B . The potato is heavier than the salt water.     C . The potato will directly sink in the fresh water.     D . The potato directly sinks in the experiment.
9. （5） What can we learn from the experiment?    

   A . Ocean water is full of salt. B . The fresh water and the salt water can't mix together.     C . Drinking salt water sometimes is good. D . Salt water can hold up more weight than fresh water.