Answer:C) Peter is exercising because he wants to be on the lacrosse team.
Explanation:
A gerund is formed when we add -ing to a verb. It functions as a noun in a sentence, while gerund/gerund phrase can be a subject or an object (direct/indirect) of a sentence. For example, gerund form of the verb 'to read' is reading.
However, gerund should not be confused with continuous tenses. In sentence - Peter is exercising because he wants to be on the lacrosse team, is exercising is not a gerund, but is a verb form, present continuous tense of verb to exercise (verb to be + ing form).