I must find out why＿＿＿＿so many students made the same mistake.
A. is it that
B. was it which
C. it is what
D. it was that
网友回答
A. is it that
B. was it which
C. it is what
(答案→)D. it was that
解析：考查强调句的特殊问句做宾语从句：句意：我必须弄清楚为什么这么多学生犯同样的错误。why引导的是宾语从句，从句中为强调句型的特殊问句。疑问词why+is it+that…，排除BC，因为是做find out的宾语，从句语序为陈述语序，B排除；所以选D。