In the argument given, the two portions in boldface play which of the following roles?
From the start we can prethink the roles of the boldfaces and then eliminate those choices that don’t support our prethinking:
We can see that the second boldface qualifies the first boldface and has some sort of relationship. The correct choice should also show this relationship.
(A) The first is a conclusion for which support is provided but is not the argument's main conclusion; the second is an unsupported premise supporting the argument’s main conclusion.
There is no main or secondary concsluion in the sentence. If there were two conclusion then usually one contradicts the other, but here no piece of info does so. The second is supported by the claim of scientists.
(B) The first is a conclusion for which support is provided; the second is another conclusion opposing the first conclusion.
The second conclusion doesn’t oppose the first conclusion. For this the second boldface should have said “it doesn’t absorb by up to 200%”. But this doesn’t happen.
(C) The first is a conclusion for which support is provided; the second is another conclusion, limiting a possible interpretation of the first conclusion.
Correct choice because because the second boldface indeed limits the interpretation of the first and says that a development doesn’t offer 200% efficiency. In other words, someone who reads the first may presuppose the that efficiency also must ncrease by 200%. But the second says that this is not the case.
(D) The first is a premise supporting the only explicit conclusion; so is the second.
The first and the second themselves are consluions made from a development. They are not premises.
(E) The first is the argument‘s only explicit conclusion; the second is a premise supporting that conclusion.
The second boldface doesn’t support the first, but instead limits the first. Hence this choice is incorrect.
Hence C