When a descriptive word, phrase, or clause is essential to the meaning of a sentence, that element is restrictive. Descriptive elements can be either restrictive or non-restrictive depending on whether they are essential or not to identify the noun they modify.
Restrictive elements provide key information to identify the noun they modify and cannot be removed from the sentence without changing its meaning. On the contrary, non-restrictive elements do not provide essential information and can be dropped without altering the sentence's meaning. That is why your answer would be restrictive.
