How will the right answer fit in terms of support and conclusion?

Only the right answer will use the same kind of support and the same kind of conclusion as the passage.

Highlight the main conclusion in the passage, if there is one:

this hypothesis cannot be correct

[BACKGROUND]. However, [CONCLUSION], since [SUPPORT]. But [SUPPORT].

Map the wording of the answers to the wording of the passage:

(A) …Indo-European cannot be the earliest language…

So what? No one said it was. In the passage, the conclusion rejects the argument in the previous sentence. This is rejecting an argument no one is making.

(B) …they cannot all be true at the same time.

That doesn’t map to the reasoning in the passage, which is that a hypothesis must be wrong because it implies something “absurd”.

(C) …and so on, without end…

This is a perfect match for the “infinite regress” explained in the passage, and “impossible” maps nicely to “absurd”. This is a keeper for sure.

(D) This definition is unfortunate…

That’s definitely not the same as concluding that “this hypothesis cannot be correct”. No way “unfortunate” maps to “cannot be”.

(E) …put together from smaller collections…

This is a different kind of support from the passage, which said something was “absurd”.

(C) is the correct answer.