Official Explanation:

Step 1: Identify the Question Type

The word “weaken” in the question stem is the clearest indication of a Weaken question.

Step 2: Untangle the Stimulus

The argument we’re seeking to weaken is that of the FDA spokesperson, who claims that the new blood clot–dissolving agent approved by the FDA could save the lives of people who would otherwise die of their heart attacks before reaching a hospital or clinic.

Step 3: Predict the Answer

The spokesperson’s conclusion can be characterized as a prediction. Before evaluating the choices, let’s determine what would have to happen in order for that prediction to come true. In order for the blood clot–dissolving agent to save these lives that the spokesperson mentions, it would have to be administered before people get to the hospital, since that’s the critical life-saving window. So to weaken the argument, we need an answer that demonstrates that this won’t happen.

Step 4: Evaluate the Choices

It doesn’t get much more straightforward than (A), which is the correct answer. If the agent must be administered in the hospital, then it doesn’t do this group of people any good, since they ordinarily die before they can get to the hospital.

(B) doesn’t weaken the argument because it doesn’t tell us that the new dissolving agent won’t help these heart-attack victims.

(C) strengthens the argument by suggesting that paramedics will have a chance to save victims without having to bring them to the hospital first.

(D) has no effect; even if there are other agents out there, that doesn’t mean that this new agent won’t be helpful.

And (E) does introduce some potentially nasty side effects, but the spokesperson doesn’t argue that the new agent won’t cause side effects; he merely argues that the drug will save lives.

Choice (A) is correct.