The official answer is B? I don't understand why?
Let me try to explain
First, the question
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 by their brightness: the greater a comets 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 Halleys comet which were base on its brightness were too low.
(C) The total amount of light reflected from Halleys 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.
(E) Scientists need more information before they can make a good estimate of the mass of Halley's comet.
Now, lets look at it both mathematically and verbally,
Mathematical situation: Brightness is directly proportional to Mass of the comet.The passage only talks about the material of the haley's comet. We do not really know anything about the other comets.
Considering this point --> A and D are outThe scientists now know for sure that the material of haley's comet reflects 60 times less light than it actually should.
So now when the scientists know about this, do they need more information to calculate the mass of haley's comet? We cant really say can we? Thus, E is also out.
Consider Option C The total amount of light reflected from Halleys comet is less than scientists had previously thought.
This is simply irrelevant, the amount of light reflected from the comet has not changed, its the same as it was observed, the scientists just got to know that the light that was reflected was less accroding to its mass. So C is also out. As stated earlier, Mass of a comet is directly proportional to Brightness it reflects,but haley's comet was not reflecting the light it should be actually reflecting(mathematically, the constant or direct proportionality that is used in the mass calculation formula does not hold good with haley's comet). Thus, the mass calculated will be much lower than the original formula gave us. B is your answer.
Hope it helped.
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