The italicized noun clause is "what i like best about the farm."
Answer: B) Subject complement.
Explanation: A noun clause is a dependent clause that acts as a noun. Noun clauses begin with words such as how, that, what, whatever, etc. Noun clauses can act as subjects, subject complements, direct objects, indirect objects, predicate nominatives, or objects of a preposition. In the given sentence the noun clause is used as a subject complement because it is placed after a linking verb (to be) and it characterizes (or gives further information) about the subject (The fresh air).