How should you support the thesis of your critical review?

The claim.

Explanation:

Let's look at what the sentence does.

"Topic [x], [y], and [z] are factors of [z]."

This is not a reason, as it doesn't attempt to explain anything.

There is no proof in the sentence itself, so it cannot be evidence.

It does not counter a previously made argument, it just sets forth a new claim - so your answer is A. The statement is a claim.