题干

下列关于声现象的说法中,正确的是(   )

A:人说悄悄话时,声带一般是不振动的

B:垂钓人的说话声会吓跑要上钩的鱼,说明水能够传声

C:街道上显示噪声等级的装置可以消除噪声

D:利用“B超”对孕妇进行常规检查时,不能向孕妇体内发射超声波

上一题 下一题 0.0难度 选择题 更新时间:2019-09-25 04:10:05

答案(点此获取答案解析)

B

同类题4

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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!