Thanks for the question! So let’s take a look at what the stimulus is saying. Corporations with frequent social events have higher profits than those that don’t on average. So, the argument concludes, you can get higher profits by having more staff parties.
Now we’re asked for something that weakens the argument. One possibility that should jump out immediately is that this is going to be a correlation/causation issue. Is it the events that cause the profits, or the profits that cause the events? Probably the profits that cause the events; companies doing better off have more frequent social events, not the other way around. (A) tells us this, and so (A) is the correct answer; it shows that the argument mistakenly thinks that X causes Y, when really, it’s more likely the other way around.
(B), on the other hand, is incorrect because it compares corporations that have staff parties during business hours vs. those that have them after business hours, which isn’t at issue in the original stimulus. The original stimulus is about having more or less staff parties, not about when to have them. So (B) brings up something irrelevant and can’t weaken the argument.
Hope this helps! Feel free to ask any other questions that you might have.