已知光的传播速度是3×108m/s，从地球向月球发出一束激光信号，经过约2.54秒收到了从月球反射回来的信号，则月球到地球的距离约（ ）
A．3.81×108m
B．7.62×108m
C．2.6×108m
D．8×108m
已知光速为：v=3×108m/s，
激光信号在地球向和月球间往返所用的时间为：t=2.54s，
激光信号通过的路程为：s=vt=3×108m/s×2.54s=7.62×108m，
故月球到地球间的距离为：
=s 2
=3.81×108m．7.62×108m 2
故选A．
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| Mr. and Mrs. Smith's house was full of suitcases, packages and packed-up boxes. The two of them were 1 with pencils and paper, checking their luggage, when there was a 2 at the door. Mr. Smith went to 3 it and saw a well-dressed middle-aged lady outside. The lady said that she lived in the house beside theirs, and that she had come to 4 them to their new home. The Smiths invited her in after apologizing for the state of the house. "Oh, 5 ," she answered. "Do you know in some parts of this 6 neighbours are not all 7 ? There are some streets where people do not 8 their neighbours, 9 their next-door ones. But in this street everybody is friends with 10 else. We are one big, happy family. I'm 11 that you will be 12 here." The well-dressed lady got a 13 when she came to visit the house the 14 time, because she found a quite 15 man and woman in it. Mr. and Mrs Smith had not had the courage to tell her that they were not the new owners of the house, who were to move in the next day, but the old ones, who have lived beside her for two years without ever having visited her or even noticing her existence (存在). | ||||
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