【单选题】The earth is much cooler than the sun, and the wave length of the earth's radiations is much longer than that of sunrays. These longer heat waves cannot pass through the atmosphere as easily as the sh...
A.
heat waves rising from the earth
B.
waves absorbed by water vapor
C.
waves sent out by radio stations that transmit local programs
【单选题】Microwave communication uses high-frequency(56)waves that travel in straightlines through the air. Because the waves cannot(57)with the curvature of the earth, they can be(58)only over short distance....