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小刚同学用焦距为10cm的凸透镜做实验,实验装置如图所示,在实验过程中保持凸透镜的位置不变,请你根据所学知识完成下列填空.

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B

    Most of us have ever imagined the life on a desert island. We sometimes imagine a desert island to be a sort of paradise(天堂) where the sun always shines. “Ripe fruit falls from the trees and you are free to sit around without any work. This is really a beautiful picture, isn't it? However, the other side of the picture is quite the opposite. Life on a desert island is awful. You either starve to death or live like Robinson Crusoe, waiting for a boat which never comes.

    Perhaps there is some truth in both these pictures, but few of us have had the chance to find out. We can only experience it in the story like the following.

    Many years ago, two men spent five days on a coral island and they wished that they could stay there longer. They were driving a badly damaged boat from the Virgin Islands to Miami to have it repaired. During the journey, their boat began to sink(下沉). They quickly put food, matches, and cans of beer into a rubber dinghy(救生筏) and rowed for a few miles across the Caribbean until they arrived at a tiny coral island.

    There were hardly any trees on the island and there was no water, but this did not seem to be a problem. The men collected rainwater in the rubber dinghy. As they had brought a gun with them, they had plenty to eat. They caught lobster and fish every day, and they thought they lived just like a king. Five days later, a tank passed by and saved them. However, they felt sorry that they had to leave