Complete the defining clause with the object relative pronoun omitted: The replacement filters ___ have arrived. Use exactly the subject we, the simple-past verb ordered, and the time phrase last week in that order, with no added words.

Explication

We supplies the clause subject, and the filters are understood as the object of ordered, so the contact clause needs no relative pronoun. Adding them would be the closest error because it would duplicate the antecedent's object role.