Hi LA,
Thanks for the question. This is going to be a tough question no matter how you approach it, exactly because of the way each answer choice starts with "if" (and on that note, this is a very tough game in general). Those "if"s are bothering you, and with good reason
You are right that the Must Be True aspect seems a bit odd, because it's a Must question where it's based on the conditional in each answer being true or not. The four wrong answers will, as you correctly state, be not necessarily true (and they could be Cannot Be True, even).
As we note in the explanations to this game, when you see a question where each answer choice starts with an "if" (which we call 5-If questions), usually the best course of action is to skip the question for the moment, and return to it at the end of the game. The reason is that as you complete the remaining questions, you will learn more about the game and probably encounter more hypothetical solutions, which you can then hopefully use to kill one of more incorrect answers. By using that approach, you can limit the number of hypotheticals you have to produce, because producing each solution yourself usually requires more time. Note: one exception to this rule is a game where you Identify the Possibilities or Templates, because those games are tailor-made to solve questions like this (the same holds true if you really felt in control of game, and thought you had a
great handle on it (not just good, but great)).
Hopefully, you can eliminate at least one or two incorrect answers by surveying the work you did for other questions, but at that point you are in a position where you have to separate answers by attempting to place the sufficient condition in its place (for example, for answer (C), start by placing U's session on Wednesday). Then, it's not that you try to start by putting Z somewhere else than Tuesday, you instead try to see if Z is forced into Tuesday. This is because in the right answer, you won't be able to avoid putting Z on Tuesday. If you can make a solution where Z ends up somewhere else than Tuesday, then as you say you know this is wrong. So, overall, you have the right idea.
The good news is that questions of this type appear not so frequently, so you won;t be forced into having to deal with this situation all that often.
Please let me know if that helps. Thanks!