Help to understand this question from reading comprehension in my GRE textbook?

Question

> *The organizers of tomorrow's outdoor concert announced that it will go on tomorrow on schedule unless bad weather is forecast or too few advance tickets are sold. If the concert is canceled, refunds will be made to ticket holders. Since some ticket holders have already been issued refunds even though more than enough advance tickets were sold, it must be the case that bad weather is forecast.*> > > **Question**> *Which of the following is an error of reasoning contained in the argument?*> > **(A)** It proceeds as if a condition, which by itself is enough to guarantee a certain result, is the only condition under which that result would occur.> > **(B)** It bases a conclusion that is known to require two conditions on evidence that bears on only one of those conditions.> > **(C)** It explains one event as being caused by another event, even though both events must actually have been caused by some third, unidentified event.> > **(D)** It treats evidence for the absence of one condition under which a circumstance would occur as conclusive evidence that circumstance will not occur.> > **(E)** Evidence given to support the conclusion actually undermines it.This is an reading example from my GRE textbook, but it doesn't offer the answer key for it(that's why I ask here). I choose **B**, because I don't quite understand it(maybe that's not a good reason to choose it). Here is my understanding for all the other options:1. [(A) It proceeds as if a condition, which by itself is enough to guarantee a certain result, is the only condition under which that result would occur.] I think A is correct, because it reflects the logic of {**If the concert is canceled, refunds will be made to ticket holders.**}2. [(C) It explains one event as being caused by another event, even though both events must actually have been caused by some third, unidentified event.] **C is correct because refunds will be made if the concert is canceled, and both refund and the concert is canceled would be caused by either bad weather is forecast or too few advance tickets are sold.**3. [(D) It treats evidence for the absence of one condition under which a circumstance would occur as conclusive evidence that circumstance will not occur.] D is correct, because it reflects {**Since some ticket holders have already been issued refunds even though more than enough advance tickets were sold, it must be the case that bad weather is forecast.**} 4. [(E) Evidence given to support the conclusion actually undermines it.] I'm not quite sure what "**it**" refers to. If '**it**' refers to **the concert event**, then I think D is also correct. Is my understanding correct? What's **B** conveying? Finally, which one should be the answer for the question?

Answer 1

In the first sentence of the passage, two if/then propositions can be deduced from the use of “unless.” These are:

1) If there’s bad weather, then the concert will be cancelled; and

2) If too few tickets are sold, then the concert will be cancelled.

Before going on, let’s note that nothing in the passage implies that the two conditions just named (bad weather; low sales) exhaust all the possibilities for why the concert could be canceled (in other words, nothing in those conditions is logically inconsistent with cancelling the concert for some other reason).

The second sentence adds this conditional:

3) If the concert is cancelled, then ticket-holders will receive refunds.

Again, before moving on, note that nothing in the 3rd condition implies that the only reason refunds would be issued is if the concert is cancelled. In other words, it doesn’t exclude the possibility that there are conditions other than cancellation that could lead to a refund being given.

Lastly we learn that some ticket-holders have actually received a refund; and that enough tickets were sold that poor sales couldn’t be the reason for concert cancellation. The argument’s conclusion is based on erring in thinking that the concert must have been cancelled, and in thinking that if it had been canceled, the only remaining reason could be bad weather. Based on the conditional propositions the passage provides, the issuing of refunds doesn’t imply the concert was cancelled at all, and so also doesn’t imply that that was due to bad weather.

Answer A is correct. The argument is based on the unwarranted assumption that just because a condition wiould guarantee a result, that it is the only condition that would bring about that result (in fact the conclusion is based on making that error at two levels - with respect to both what could cause cancellation and with respect to what would could cause a refund to be issued).