The correct answer is B. The James Madison Memorial Building, built in 1981, houses the Folger Shakespeare Library.
Explanation:
In grammar, a nonessential element is a word or set of words that provide information about a previous noun or any other element in the sentence. This is considered as nonessential because it provides extra information but it is necessary to have a complete sentence, because of this, in most cases commas are placed to enclosed the element, which means a comma is placed before and after the nonessential element. In the case, fo the sentence presented the words that only provide extra information are "built in 1981" and therefore the correct option to separate the nonessential element is "The James Madison Memorial Building, built in 1981, houses the Folger Shakespeare Library".
