The correct answer is D. The window in the living room provides the best natural sunlight.
Explanation:
A restrictive phrase, also called defining clause is a clause containing essential information about the subject of the sentence, this implies, this information is necessary and cannot be removed as in the case of non-restrictive phrases, due to this, the additional information provided is never separated from the main sentences by using commas (,), parenthesis () or similar punctuation marks, in the case of "The window in the living room provides the best natural sunlight", the main phrase is "The window provides the best natural sunlight" and "in the living room" is information that has been added an cannot be separated from the main sentence, also as this is not marked by any punctuation marks the information is essential to describe the subject and thus, this is a restrictive or defining phrase or clause.
