[单项选择]Of all the problems facing modern astronomers, perhaps the most fascinating one is "can intelligent life exist elsewhere" Since the earth is a unimportant planet moving round an unimportant star, it would be a pride on our part to suppose that we are the only intelligent beings in the universe. But to obtain proof is difficult.
The main trouble is that our neighbor worlds, the bodies in the Solar System appear to be unsuitable for advanced life forms. The Moon may be ruled out at once; it has hardly any atmosphere. Venus is little better; the surface temperature is extremely high and the atmosphere is mostly carbon dioxide. Mars with a very thin atmosphere and a severe shortage of water, may well support simple that life seems no hope of finding animals, while the alternative Martians of the story-tellers have since been given up.
Of course this has not stopped the flow of bright ideas of communicating with the supposed people on Mars. In the early nineteenth century the grea
A. there may be other intelligent beings in the universe
B. there are other intelligent beings in the universe
C. people living on the earth are almost certainly the only intelligent beings in the universe
D. people living on the earth are definitely the only intelligent beings in the universe