单选题It was when searching&nbs

问题补充：

单选题Itwaswhensearchingforthelostbookwhosecoverwasmissing______asecretletteraddressedtohismother.A.what he foundB.until he foundC.that he foundD.he had found

答案：

C解析考察强调句型。本题是一个强调句型，强调的是时间状语when searching for the lost book whose cover was missing，强调句型的后半句使用陈述语序。故C正确。