Bài mẫu Reading của TOEFL - bài 4
Luyện thi TOEFL
Bài mẫu Reading của TOEFL - bài 4
The basic principle of radar is exemplified by what happens when one shouts in a cave. The echo of the sounds against the walls helps a person determine the size of the cave. With radar, however, the waves are radio waves instead of sound waves. Radio waves travel at the speed of light, about 300,000 kilometers in one second. A radar set sends out a short burst o...
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