练习材料：
Lesson43-3 Are there strangers in space?
Such a messenger, receiving our radio and television signals, might well re-transmit them back to its home-planet, although what impression any other civilization would thus get from us is best left unsaid.
But here we come up against the most difficult of all obstacles to contact with people on other planets -- the astronomical distances which separate us. As a reasonable guess, they might, on an average, be 100 light years away. (A light year is the distance which light travels at 186,000 miles per second in one year, namely 6 million million miles.) Radio waves also travel at the speed of light, and assuming such an automatic messenger picked up our first broadcasts of the 1920's, the message to its home planet is barely halfway there. Similarly, our own present primitive chemical rockets, though good enough to orbit men, have no chance of transporting us to the nearest other star, four light years away, let alone distances of tens or hundreds of light years.
应用配置：L0+L4
知识笔记：separate/ barely/ orbit/
练习感悟：用时35分。晨读。最后一版还是有几个单词读错，没再调整。
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