<span id="docs-internal-guid-64fea607-7fff-5c8c-f5f6-32f9953e0efc"><p dir="ltr">Let’s focus on the adjective clause, “_______ requires extensive experience.” The blank should be filled with a subject relative pronoun that modifies a thing or things to complete the adjective clause. For this reason, (C) "which" is the correct answer. <br></p><p dir="ltr"><span style="color: rgba(0, 0, 0, 0.87);">(B)</span><span style="color: rgba(0, 0, 0, 0.87);"> "who"</span><span style="color: rgba(0, 0, 0, 0.87);"> can serve as a subject relative pronoun in an adjective clause, but it modifies a person or persons, not a thing or things. (A) "</span><span style="color: rgba(0, 0, 0, 0.87);">whoever"</span><span style="color: rgba(0, 0, 0, 0.87);"> and (D) "</span><span style="color: rgba(0, 0, 0, 0.87);">whatever"</span><span style="color: rgba(0, 0, 0, 0.87);"> are incorrect because when used in an adjective clause, they are compound relative pronouns that combine the antecedent and the relative pronoun that modifies it. “Whoever” means “anyone who,” while “whatever” means “anything that.” But the antecedent already exists in this question, and only a subject relative pronoun is missing.</span><br></p></span>