When I first saw this question it was frustratingly confusing. But, coming back to it and being able to map out the argument and understand what they are saying their argument is actually quite bad. Aha.

For people who chose D this may help:

D is saying that an INDIVIDUAL MEMBER of the alliance failing to perceive an economic threat will have a weaker policy IN THEIR NATION. We do not know that because the entire argument is about a threat to the ALLIANCE'S ECONOMY.

C makes sense because it says some will view it as a threat and others will not meaning THE ENTIRE ALLIANCE will not agree and therefore be weaker for it.

Tricky wording that did perturb me a bit.

Sometimes you have to activate your domain expansion.