What transition word should I use in this sentence?
"However" is the correct answer.
The SAT is a standardized test, which means that there can only be one correct answer.
"In fact," "moreover," and "indeed" all mean the same thing. This means that they must be wrong.
Since the test is objective, you will never have to choose the "better" answer out of two (or more) options. Instead, three of them will be completely wrong, and one will be completely right; there is no in-between.
"However" is the only answer that opposes what has been previously written, whereas the other three simply add to it.