When we're asked to EVALUATE an argument, we must first determine how the argument is logically flawed.

Premises:
- Because of a rare type of fungus that killed off many cacao trees in Brazil, there was an unusually meager harvest of cacao beans this year.
- The wholesale price of cocoa solids and cocoa butter has increased significantly and is unlikely to fall in the foreseeable future.

Conclusion:
- As a result, the retail price of chocolate is certain to increase within six months.

Missing information:
- is the price of cocoa the only thing that affects the price of chocolate? What about sugar, milk, etc?
- is it possible for the chocolate companies to accept a smaller profit margin?
- is the timeline right? Is the price of chocolate in 6 months based on the price of cocoa now? Or might there be stockpiles of cocoa, so it won't affect the price for a few years?

We're looking for a question for which a YES answer would WEAKEN the argument, and a NO answer would STRENGTHEN (or vice versa):

(A) Has the price of cocoa solids and cocoa butter remained steady during other periods of poor harvest?
- if yes... our conclusion about 6 months from now could still hold, because we already know that the price went up.
- if no... that still doesn't matter to our current situation

(B) Are consumers willing to spend more for chocolate?
- if yes... this could support the idea that the price will go up
- if no... the price might still have to go up, if the price increase on cocoa eats into (pun intended) the entire profit margin. People might not buy as much, but the company may not have a choice.

(C) Have the prices of other ingredients in chocolate decreased recently?
- if yes... this weakens the argument. The price might be able to stay the same.
- if no... this strengthens the argument. It makes it more likely that the price will indeed go up.

(D) What percentage of cacao trees in Brazil were affected by the fungus?
This is irrelevant. We're already told that it's "many" trees - enough to significantly impact the price of cocoa. What that represents as a percent of the total won't impact the argument one way or the other.

(E) Can the fungus be eliminated within the next six months?
- if yes... this could impact cocoa prices further down the line, but we don't know if it impacts the price of chocolate in 6 months.
- if no... nothing changes about our argument.

The only question that helps us to evaluate the validity of the argument is C.