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：句意：Leo永远不会忘记的那一刻是他加入空军的时候。第一个是定语从句，修饰moment，关系代词做宾语，用that或which;第二个是表语从句，引导词做时间状语，用when。故选C。