This is a sufficient assumption question but one of the forums I read to understand answer choice (A) explained that NEGATING (A) would demonstrate it to be a sufficient assumption. I totally see that negating (A) would weaken the argument, but I thought we use negation test for necessary assumption questions ...or am I not aware of some exceptions? I know that for some flaw questions that contain "takes for granted/assumes that" language, you can negate the answer choices, but I never heard of using negation test for sufficient assumption questions.
Comments
This is also why the negation test works here.
I might not have paid sufficient attention, but think I've only encountered one other question where they use both "must be true" and "be properly drawn", and fell in the nicely laid trap by not reading the stem carefully. It is crucial to understand that "must be true" makes it by definition a "necessary" assumption - don't be tricked by the presence of "properly drawn" into confusing it with a sufficient assumption.