题干

某研究性学习小组设计了如右图Ⅰ所示的装置,探究空气中氧气的体积分数,其中A是底面积为5cm2、圆筒状玻璃容器(带密封盖),上面标有以cm为单位的刻度,B是带刻度的敞口玻璃管(其他辅助装置略)。他们的操作过程如下:

 

a.连接装置

b.                      

c.加入水并调整B的高度,使A、B两侧液面相平,此时A中的液面于刻度15cm处;

d.将过量的白磷放在惰性电热板上,盖紧密封盖;

e.通电加热白磷至充分反应;

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    Captain(船长)Nemo invited me and my friends to go hunting with him in the forests of Crespo Island. I asked him why he was so interested in Crespo Island. “I thought you preferred the sea to being on land.”

    “I do,” replied the captain. “But these forests are under the sea.”

After going through a door, we were about ten meters under the water. The light from the sun reached us. Everything looked very colourful. We were going deeper and deeper. At 100 meters deep, we could see quite well, and Captain Nemo stopped and pointed to some dark shapes. This was the forest. The “trees” in the forest were giant seaweed, and all their “branches” were vertical(垂直的).We could not stop looking at them. Fish swam around the branches like birds in a forest.

    Suddenly, I saw a large sea spider about a meter tall. It was going to attack me. Captain Nemo's man killed it with his gun, but it reminded me that the sea could be as dangerous as it was beautiful. When we reached 150 meters, it was dark. The sun's light could not reach this depth(深度). We turned our lights. We could see about 20 meters around us. Finally, we found Crespo Island—where a steep rock wall rose in front of us.

    We could go no further, so we walked back toward the Nautilus. Suddenly, Captain Nemo stopped and shot an animal with his gun, it was a beautiful and rare sea otter. At last, we could see the Nautilus. Several large sharks swam over us. Luckily they didn't see us. We re-entered the Nautilus safely. I was tired but amazed by what I had seen.