The two things _____ he wasn't sure were the grammar and the idioms.A. about whichB. about that C. in whichD. at which选择哪一个?为什么?
问题描述：
The two things _____ he wasn't sure were the grammar and the idioms.
A. about whichB. about that
C. in whichD. at which
选择哪一个?为什么?
答
A
be sure about 对某事肯定、确认（但没有be sure at/in的结构）
这是定语从句，先行词是things，将其还原到后面的定语从句中看充当什么成分：
he wasn't sure (about the things)
有介词后面的引导词必须用which，that不可以，A正确
答
选A。
be sure about sth.属于短语的固定搭配。因为是一个定语从句，且包含介词，所以不能用about that。
答
A
定语从句 be sure about 对.有把握 缺个about 所以从 A,B 中选
再,介词前置,不可用that 所以选A
请及时采纳,不懂继续问( 天天在线 ）
答
A 引导词前如果有介词不能用that
be sure about sth介词about提前