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.

The answer is "The officials revised the rules, which the coach explained to us before practice."

Explanation:

A dependent adjective clause is a group of words containing a subject and a verb. It offers further description or information - similar to what an adjective does - about a noun or pronoun that was mentioned in the main clause. Nonessential adjective clauses are literally not essential for the main clause to make sense. They merely offer extra information about it. A good way to tell nonessential clauses and essential ones apart is by looking for commas. Essential adjective clauses do not take commas, nonessential ones do - in fact, they must be separated from the main clause by a comma. Something else is that fact that nonessential clauses cannot be introduced with the word "that", but essential ones can.

In the last option, we have the adjective clause "which the coach explained to us before practice" modifying the noun "rules". It is separated from the main clause by a comma and the word "which" cannot be "substituted" by "that" because of such comma. Therefore, we a have a nonessential adjective clause.

an expression designed to call something to mind without mentioning it explicitly; an indirect or passing reference.

3 is blunder, i’m not sure about the last one but the first two look correct