问题
选择题
It was when searching for the lost book whose cover was missing ______ a secret letter addressed to his mother.
A．what he found
B．until he found
C．that he found
D．he had found
答案
答案：C
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。