The correct answer is A. Gerund
Step-by-step explanation:
In grammar, the gerund and the present participle are both types of words derived from verbs and that end in -ing. For example, the words "playing", "fishing" and "golfing" can work either as a gerund or as a participle. However, there is a big difference between the function of each one, in the case of gerunds the word that ends in -ing work as a noun, which is usually the subject of a sentence; on the other hand, in the case of participles these words work as a verbs or even and adjective. Considering this, in the case of the word "Golfing" from the sentence "Golfing can be an expensive hobby", it can be concluded this word is a gerund and not a participle because "Golfing" refers to a noun and indeed is the subject or agent that performs the action "can be" instead of acting as an adjective or verb.