This Main Point question may be a bit difficult because it does not have many premise/conclusion indicator words. We must remember that it is still an argument, so we should ask ourselves what the main point was before reading the answer choices.
Recall that a main point is an author's statement that is receiving support but not itself supporting anything. Answer choice A is alluding to the second sentence, where it says “not the first evidence of life has been forthcoming”. If this is, in fact, the main point, we would expect to find another sentence that provides evidence in support of this one. The following sentences talk about the future, so they cannot provide evidence for what happened in the past. Since nothing supports this sentence, it cannot be the main point.
We then can ask the same thing about the final sentence. Does it receive any support? In this case, it is supported by the previous statements, that no evidence has been found, and that we have no reason to believe that it ever will be found.
The argument is obviously not bullet-proof, but it need not be. The final sentence is at least receiving some support, while the others are not.
Only after identifying the main point should you go to the answer choices. Simply find the answer that best matches your prediction. In this case, C is a great match.
