Complete the comma-set clause with a four-word fragment: The east wing, ___, will remain closed. Use which followed by the verb houses and the noun phrase the archives, with no added words.
Bonne réponse
which houses the archives
Explication
Which refers to the east wing and acts as the subject of houses in the parenthetical clause. Omitting which would be the closest error because non-defining clauses require an expressed relative pronoun.