题干

如图所示,平行板电容器的A板带正电,与静电计上的金属球相连;平行板电容器的B板和静电计的外壳均接地.此时静电计指针张开某一角度,则以下说法中正确的是(   )

A:在两板间插入介质板,静电计指针张角变大

B:在两板间插入金属板,(金属板与A,B板不接触)静电计指针张角变大

C:B板向右平移,静电计指针张角变大

D:B板向上平移,静电计指针张角变大

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D

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    Imagine you are in a jumping contest. Animals and insects can also enter this contest. But they might just leave humans in the dust!

    The first event is the long jump. The human athlete is Mike Powell. In 1991, he jumped nearly 30 feet, which is the world record for the long jump. That is about five times his own height.

    His competitor in the long-jump contest is a frog named “Rosie the Ribbiter.” Rosie set the world record for frogs in 1986 by jumping more than 21 feet. Her record has never been broken by any other frog. Compared to Mike Powell, Rosie's jump is not that amazing. But wait! Rosie is only about 10 inches long when her legs are stretched to their full length. She can jump more than 25 times her size. Rosie, the frog, wins the long-jump event.

    The next event is the high jump. Javier Sotomayor, the world record holder, can jump a bar (横杆) 8 feet high. That is about as high as the ceiling in most homes.

    Looking around for someone to challenge his record, Javier might need a magnifying glass (放大镜). The next contestant is a tiny insect called the spittlebug (吹沫虫).

    The spittlebug can jump 28 inches into the air. It is only a quarter-inch long, less than the width of a pencil. If the spittlebug were the same size as Javier, it would be able to jump 600 feet into the air. That is like a human jumping over a building 55 stories high!

    Though the humans lose the “jumping contest,” their competitors would probably agree that Mike and Javier are still pretty excellent athletes. If only Rosie and the spittlebug could speak!