题目

One day,Raul was miles away from the small ranch（牧场） house in a large valley. 1  seemed to be all right,yet he felt strange and somewhat uneasy.The wind had picked up,and angry,dark clouds  2  across the sky. He could smell the rain coming.And it did. 3 ,the lightning flashed through the clouds,nearly  4  Raul.The thunder（雷声） was so loud that he buried his  5   in his hands and rubbed his eyes.Then he heard it. Hoofbeats（蹄声）.He  6 .There before him stood a tall, white  7 . An old man stared down at him from its back. “Wh-wh-who are y-y-you?” asked Raul.“如图所示的电容式话筒就是一种电容式传感器，其原理是：导电性振动膜片与固定电极构成了一个电容器，当振动膜片在声压的作用下振动时，两个电极之间的电容发生变化，电路中电流随之变化，这样声信号就变成了电信号，则当振动膜片向右振动时：（ ）A．电容器电容减小 B．电容器带电荷量减小C．电容器两极板间的场强增大 D．电阻R上电流方向自左向右