A-A+
This is an important problem _______ too few s
问题详情
This is an important problem _______ too few social scientists have researched. A. which B. that C. into that D. into which
参考答案
正确答案：D
into which引导的是problem的定语从句。which指代problem，into与research搭配。（本解析由学员提供）
