There are two types of adjective clauses: Restrictive and Nonrestrictive adjective clause. A nonrestrictive adjective clause consists of words within the sentence that can be omitted, but not changing or affecting the meaning of the sentence. These clauses are usually separated by a pair of commas. On the other hand, restrictive clause is the opposite.
In the options given, the sentence that contains a nonrestrictive adjective clause is: The sandwich, which had been prepared hours earlier, was soggy and unappetizing.
