Question

Which sentence contains a nonessential adjective clause? The coach explained the rules that the officials revised in 2010. The coach who is an expert in the sport explained the revised rules to us. After explaining the rules to us, the coach released us to the field. The officials revised the rules, which the coach explained to us before practice.

Answer 1

The answer, in my opinion, is the second sentence, "The coach who is an expert in the sport explained the revised rules to us". Here, the "Who is an expert", is presumably the nonessential clause. 

Answer 2

B. The coach who is an expert in the sport explained the revised rules to us.

Step-by-step explanation:

The adjective clause exemplifies the modifier of the noun clause that contains both a subject and a verb and begins with a relative pronoun. The sentence contains a nonessential adjective clause is the second option. It carries unnecessary adjective clause, i.e. "who is an expert in the sport" as it describes the coach unreasonably. If he is a coach, the description mentioned here is quite obvious and understood. Thus, it is not required to mention it. Hence, the B option is the answer.