How will the right answer fit in terms of support and conclusion?

Only the right answer will accurately describe the support and/or conclusion. That will also make it the only one to call out why this support doesn’t establish this conclusion.

Highlight the main conclusion in the passage, if there is one:

it was not wrong for Meyers to take it.

Lawyer: [SUPPORT], and [SUPPORT]. However, [SUPPORT], so [CONCLUSION].

You want to recognize that the support here is a combo of an if-then rule and a fact about Meyers. That tells you it’s pretty much 100% that the argument’s flaw is mixing up the sufficient and necessary conditions. Arguments can do that in two different ways, but those details don’t necessarily matter. Take a look at the answers. How many of them even talk about sufficient and necessary conditions?

Map the wording of the answers to the wording of the passage:

C) takes a condition that by itself is enough…to also be necessary…

Just one! Enough is a synonym for sufficient. The details in this answer about an action being wrong also match what the passage talks about. Now on test day, that wants to be good enough. You get the same points whether you can explain why (C) is correct or not! That said…

The passage says if you take something you think belongs to someone else, that’s wrong. Meyers didn’t think the compost belonged to someone else. But that doesn’t mean there couldn’t be some other reason that taking the compost was wrong. If there is another reason, then it isn’t necessary to think it belongs to someone else for taking it to be wrong.

But the conclusion says that it wasn’t wrong, based only on that one reason. So the author is assuming that’s the only possible reason. In other words, they’re saying that reason IS necessary. Which is a flaw. And that, in it’s charmingly confusing way, is what (C) says. Let’s make sure we also agree the others are wrong.

(A) confuses a factual claim with a moral judgement.

The conclusion makes a moral judgement, and it’s based on a factual claim. No confusion though.

(B) …if he had good reason to believe that it was someone else’s property

This condition doesn’t come up in the passage, so be careful. It only talks about a situation in which Meyers does NOT have reason to believe…

(D) fails to consider the possibility that the compost was Meyers’ property

We’re told explicitly he didn’t have any reason to think it was someone else’s property, which actually covers the more specific possibility that it’s his compost. So I don’t think it’s fair to say the lawyer “fails to consider” this. Not that it would affect the argument anyway. So not a flaw in any case.

(E) concludes that something is certainly someone else’s property…

No it doesn’t, it concludes that something isn’t wrong.

(C) is the correct answer.