The moment Leo will never forget is he joined the Air Force
A. when; that
B. that; that
C. that; when
D. when; /
网友回答
A. when; that
B. that; that
(答案→)C. that; when
D. when; /
解析：考查从句辨析。第一格是定语从句，先行词是The moment，在定语从句中做宾语，故用关系代词that；第二格是表语从句，由于主语是the moment，所以应用when引导表语从句，句意：里奥永远不会忘记的时刻是他参加空军的时候。选C。