Total contributions by individuals to political parties were up 25 percent in this most recent presidential election over those of four years earlier. Hence,

it is obvious that people are no longer as apathetic as they were, but are taking a greater interest in politics.

Which of the following, if true, would considerably weaken the preceding argument?
(A) The average contribution per individual actually declined during the same four year period.
(B) Per capita income of the population increased by 15 percent during the four years in question.
(C) Public leaders continue to warn citizens against the dangers of political apathy.
(D) Contributions made by large corporations to political parties declined during the four-year period.
(E) Fewer people voted in the most recent presidential election than in the one four years earlier.

I'd go with E.

If less people voted that might indicate that people are taking less interest in the politics even if total contribution increased.

Ok let's do it by POE.

(A) The average contribution per individual actually declined during the same four year period.
This only means more people have contributed, which strengthens the conclusion that people are more interested.

(B) Per capita income of the population increased by 15 percent during the four years in question.
This would be the best answer, in my opinion, if the number is 25 or more. Since it would indicate that the increase in political contribution is only comparable to the increase in people's income. However since 15<25, it still follows people must be more interested than before.

(C) Public leaders continue to warn citizens against the dangers of political apathy.
That says nothing about if people are more interested.

(D) Contributions made by large corporations to political parties declined during the four-year period.
This again strengthens the conclusion. If corporation contribution declined while total contribution increases, that must mean more contribution from people, thus more people interested in politics.

(E) Fewer people voted in the most recent presidential election than in the one four years earlier.
Voting is another important indicator of people's interests in politics. This fact presents an counter argument to the author's argument and thus weaken the conclusion.

I will go with (E). as for (A) Total contributions increased by 25% but avg contribution per person has decreased according to (A), which implies that number of people who contributed has increased ...which will actually strengthen the argument above. The choice (E) though itself weak definitly weaken the argument.

OA is (E)
What about (A)? (A) means people actually put in less money, but the total is higher b/c of the incease in population??
(C) is flawed when we talk about the change in population also b/c fewer people voted is due to a decrease in population. What if the percentage of voters is still high?

It seems a little hard to me.
In the passage, the increase in total contributions made by individuals
and the decrease in the average contribution mean the number of population must increase. And increase in the population just weaken the argument; that is, the reason is not because of greater interest in politics but because of increase in population. doesn't weaken?

To me, E is out of scope. The vote rate doesn't necessarily mean people's attitude toward politics, it probably is weather factor which influences the vote rate.

Could anybody give me some help?

We need not break the connection. But, if we can negate the assumption then also we can weaken the argument, this is what I believe is happening in (E).

By an increase in total of 25% the author indicates awareness in more people which also means that he assumes that it is because of more people contributing (and not because more contri per person).

Statement (E) just states that no of people Dec. i.e. it negates the assumption .... do I make any sense to anybody ???