题干

两个偏振片紧靠在一起,将它们放在一盏灯的前面以致没有光通过.如果将其中的一片旋转180º,在旋转过程中,将会产生下述的哪—种现象(       )

A:透过的光的强度在整个过程中都增强

B:透过的光的强度先增强,然后又减少到零

C:透过的光的强度先增强,然后减少到非零的最小值

D:透过的光的强度先增强,再减弱,然后又增强

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B

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    Do you know any 9-year-olds who have started their own museums? When Theodore Roosevelt was only nine, he and two of his cousins opened the "Roosevelt Museum of Natural History". The museum was in Theodore's bedroom. It had a total of 12 specimens. On display were a few seashells, some dead insects, and some birds' nests. Young Roosevelt took great pride in his small museum.

    Born in New York in 1858, Theodore Roosevelt was not always healthy. "I was a sickly boy", he once wrote. Roosevelt had a health condition called asthma. He often found it hard to breathe. Instead of playing, he watched nature and then read and wrote about it.

    Roosevelt's interest in nature sometimes got him into trouble. Once, his mother found several dead mice in the icebox. She demanded that the mice be thrown out. This was indeed "a loss to science", Roosevelt said later.

    Because Roosevelt was often sickly as a boy, his body was small and weak. When he was about 12, his father asked him to improve his body. Roosevelt began working out in a gym. He didn't become strong quickly. But he did decide to face life's challenges with a strong will. That determination stayed with Roosevelt his whole life. And eventually his body did get strong. As an adult, he was an active and healthy person. He enjoyed adventures, and he loved the outdoors.

    A toy company named the teddy bear for Theodore "Teddy". After knowing that, Roosevelt refused to shoot a baby bear while hunting.

    In 1900, at the age of 41, Roosevelt was elected Vice President. A year later, President McKinley, was shot and killed. Roosevelt became our 26th President. At 42, he was the youngest leader the country had ever had.