問題詳情
27. ______ in banks and government buildings, video surveillance systems have become standard equipmenteven for the smallest convenience stores.
(A)Seeing once mainly
(B) Having seen once
(C) Once seeing mainly
(D)Once mainly seen
參考答案
答案：D
難度：適中0.405063
統計：A(6),B(13),C(16),D(32),E(0)