16. Comets do not give off their own light but reflect light from other sources, such as the Sun. Scientists estimate the mass of comets by their brightness: the greater a comet’s mass, the more light that comet will reflect. A satellite probe, however, has revealed that the material of which Halley’s comet is composed reflects 60 times less light per unit of mass than had been previously thought.
The statements above, if true, give the most support to which one of the following?
(A) Some comets are composed of material that reflects 60 times more light per unit of mass than the material of which Halley’s comet is composed.
(B) Previous estimates of the mass of Halley’s comet which were base on its brightness were too low.
(C) The total amount of light reflected from Halley’s comet is less than scientists had previously thought.
(D) The reflective properties of the material of which comets are composed vary considerably from comet to comet.（B）
(E) Scientists need more information before they can make a good estimate of the mass of Halley’s comet.
答案是B
在做这道题时有一个前提，就是照射在halley上的光的亮度不变，设光的亮度为T，以前的质量为M1，以后的质量为M2，那么T/M1=60T/M2，于是M2=60M1，那么以前的质量肯定是比以后的质量要小的，
但是文中并没有出现“照射在halley上的光的亮度不变”这个前提，
没有这个前提存在，答案还能是B吗？
GMAT&GRE&LSAT -- TEST 7--Section 1--16
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