单项选择题
The most exciting question of all is "Does life exist beyond the earth" In recent years the trend has been toward the hypothesis (假设) that life is probably a normal phenomenon wherever the conditions are fight, with the added qualification that proper conditions are not necessarily only those of the earth. It was long held, for example, that life on the planet Jupiter (木星) is impossible because of its extreme cold, crushing gravity (重力) and poisonous atmosphere. But there is evidence that the giant planet is warmer below the outer, cold layers than was first thought. The combination of gases in its atmosphere could produce organic (有机的) or preorganic (有机生物的) molecules. Since no one really knows all combinations of conditions under which life can evoke (产生), it is best to be conservative (保守的) about denying the existence of life on any planet.
Life on the planet Jupiter is a possibility which (). A. does not exist
B. should not be ruled out
C. excites all scientists
D. has never been explored