There are many advantages TO learning English. He has the advantage OF knowing English. What is the advantage OF/TO learning English? There is no logical reason to use one over the other. With prepositional phrases, it is just how the language develops.

OF I wouldn't even use this sentence as it makes little sense anyway. You say there are advantages TO something when you are comparing it against something else. As your sentence stands there appears to be no comparison, so it is rather meaningless.

The correct answer is TO.

correction* uses

Also, I have a TOEFL book. In that book, the author use preposition OF after the word "advantage"