To which Critical Reasoning question type does the following question stem belong?
"The statements above, if true, best support which of the following as a conclusion?"
Correct!
In Conclusion Strengthening questions, the conclusion appears in the argument and the question stem refers to it as the above conclusion, the argument's conclusion, or the author's conclusion.
This question, on the other hand, asks us to evaluate a conclusion that has not yet been presented and that will appear in the answer choices - that's what the wording "support which if the following as a conclusion" implies.
Assumption questions ask you to find an underlying assumption and usually include the word assumption or underlie/underlying. This questions deals with a conclusion, not with an assumption.