18. The researchers found the participants ______ significantly better when exposed to authentic input. (A)perform (B)to perform (C)performing (D)performed

17. The belief ______ learners develop grammatical competence primarily through exposure has been challenged by researchers ______ conclusions, which several critics contend ______ insufficiently grounded, have influenced current pedagogical practices. (A)that / whose / are (B)which / that / are (C)which / whose / is (D)that / which / is