A positive correlation has been found between the amount of soot in the atmosphere of cities and the frequency of a c...

Ravi on June 2, 2019

@HAMEE-YONG,

Great question. Let's look at (B) and (C).

(B) says, "If the ailment rarely occurs except in cities in which
there are large amounts of soot in the air, then the soot is probably
the cause of the ailment."

(B) is a tempting answer choice, but it has a large flaw. We know from
the stimulus that the disease correlates with the amount of soot in
the air, but we do not know whether or not the disease rarely occurs
except when there is a lot of soot. For this reason, we can get rid of
(B).

(C) says, "In each of the cities where there are large amounts of soot
in the air but little other air pollution, the frequency of the
ailment is at least as high as it is anywhere else."

(C) tells us that where there is a lot of soot but very little other
pollution, people still get the disease. (C) provides us with the
effect (the disease) without the suggested cause (other air
pollutants), so it weakens the argument by suggesting soot is to
blame. Thus, (C) is the correct answer choice.

Hope this helps. Let us know if you have any more questions!