Answer:
The sentence which contains a restrictive clause is the following one:
A. They decided to meet where the band was performing.
Explanation:
Restrictive clauses are those which cannot be separated from a main clause, since they provide identifying information, and because of that they are considered to be essential. Non-restrictive clauses are exactly the opposite: they are not essential, since they provide additional information only, as opposed to essential.
Therefore, in the sentence: "They decided to meet where the band was performing", we have a restrictive clause in "the band was performing", since it tells us where "they" (the subject of the sentence) decided to meet. There are two clauses actually:
Clause 1: They decided to meet
Clause 2: the band was performing.
The clauses above are joined by the connective "where".
The other alternatives show examples of additional information that comes between commas, as in:
The girls, overwhelmed by the sale, bought many shoes.
In the sentence above, if "overwhelmed by the sale" is dropped, there is no loss in the completeness of the sentence. In other words, there is no restrictive clause there.
