8. Man and animals cannot live without     (氧氣) .

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  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 weight than fresh water. See for yourself!You will need：

. 3 cups of warm water

. Measuring cup (跫杯)

. Wide-mouthed jar

. Sail

. 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 (攪拌) 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 liquids will not mix together. 

5. Gently place the potato into the jar. Donot 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 only halfway down.

1. In the experiment,what should you do right after you pour the water over the spoon?

   A. Add ihe salt to the water.

   B. Stir the salt into the water.

   C. Place the potato in the jar.

   D. Pour warm water into the jar.

2. In Step 4 of the experiment,why do you pour the water over the spoon slowly?

   A. It is easier to see what you are doing.

   B. It pushes the fresh water to the bottom.

   C. It will keep the water from coming out.

   D. It will keep the liquids from mixing together.

3. In which step of the experiment do you add the salt?

   A. Step 1.  B. Step 2. C. Step 3.  D. Step 4.

4. What does the underlined word Gently" mean?

   A. Carefully.

   B. Quickly.

   C. Secretly.

   D. Silently.

5. What is the most important detail about salt water in this text?

   A. You can make it yourself.

   B. You can find it in the ocean.

   C. It is heavier than fresh water.

   D. A potato will sink in it.

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 This drink is         three different sorts.

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3. 他為在奧運(yùn)會(huì)中獲得金牌而感到驕傲。 

He         he has won the gold medal in the Olympic Games.

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