Final answer:
The infinitive phrase "To recover from a tragedy" in the sentence functions as the subject, which is option D.
Step-by-step explanation:
The function of the infinitive phrase "To recover from a tragedy" in the sentence "To recover from a tragedy takes time" is indeed the subject of the sentence. In English grammar, an infinitive phrase can function in several ways within a sentence: as a noun, an adjective, or an adverb.
However, when an infinitive phrase acts as the main character or doer of the action and is what the sentence is about, it is functioning as the subject. Therefore, the correct answer to the question would be option D. Subject.