Hey Jon,
This is a Parallel Reasoning question, where the stimulus contains conditional reasoning. In its most simplified form, the argument can be diagrammed as follows:
Premise 1+2: Joe's car vacuumed 
K & L vacuum it Joe took the car to have it fixed (conditional premises)
Premise 3: Joe's car vacuumed (factual premise)
Conclusion: Joe took the car to have it fixed
Essentially, we have a conclusion containing an additive inference from the chain relationship established by the premises. We are looking for the same pattern of reasoning, where the author observes that A
B
C, and concludes that if A occurred, then C must have occurred as well. That pattern of reasoning is restated in answer choice (A):
Premises 1+2: Glass wet Emily drank from it this morning Takes medication
Premise 3: Glass wet (note: the first clause of the first sentence establishes this fact)
Conclusion: Emily took her medication
In understanding the conditional structure of answer choice (A), it is important to recall that "only if" is a necessary condition indicator, suggesting that drinking water in the morning is a necessary condition for Emily's glass being wet. In addition, the statement "the only time she drinks water in the morning is when she takes her medication" establishes "taking medication" as the necessary condition for "drinking water in the morning." It is not surprising to find the factual premise (Emily's water glass is, in fact, wet) buried in the very beginning of the argument, i.e. where you least expect to find it. The order of premises and conclusion(s) need not be matched in the correct answer choice; it is the argument structure, not the order of presentation, that is of any importance.
Hope this clears things up!
If you need additional help with conditional reasoning, please consult the Homework to Lesson 2 of our course book, or the relevant chapters in the Logical Reasoning or Logic Games Bibles.
