This is a cause and effect question .

Cause --------> Effect

X causes ---------> Z .

Now we need to support the new report that makes the claim and any premise that eliminates the others factors that causes Z and proves that Z is caused only when X occurs is the correct answer .

choice (A) dose exactly that it shows that when X occurs Z too occurs and Y dose not . So we can definitely say X causes Z.

Where as in option (E) which is a very close contender also says that Z is preceded by X and Y so we can not definitely say

If Z is caused by X or Y or both X and Y .

Same problem is repeated in choice (B)


Option C shows Y causes Z and in fact weakens the argument.

Same for D weakens .

Correct is (A)

IMO A