Alex always does warm-up exercises before he begins jogging. How is the word in bold being used? A. adverb B. subordinating conjunction C. preposition

The answer is B. subordinating conjunction

Based on the sentence, assuming that the word in bold is "before", this word functions as a subordinating conjunction. In the sentence, "before" means previously to the time of jogging. Also, it connects the two independent clauses, " Alex always does warm-up exercises" and "he begins jogging"