The moment Leo will never forget is Mr. Smith gave him a lot of valuable advice on how to improve his writing.
A. that; that
B. when; that
C. when; /
D. that; when
网友回答
A. that; that
B. when; that
C. when; /
(答案→)D. that; when
解析：经过分析句子结构可知，这个句子中包含了一个定语从句和一个表语从句。在定语从句中，关系词指物，并且在定语从句中作宾语，故用that；在表语从句中，表语从句中的引导词在从句中作时间状语，故用when。故选D。