問題詳情
17. For a long time, scientists have trouble explaining how young children can learn the grammatical rules andsounds _______ to communicate in words.
(A) require
(B) requiring
(C) required
(D) requires
參考答案
答案：C
難度：困難0.352941
統計：A(1),B(5),C(6),D(2),E(0)