Question

2. The moment__________ John will never forget is Mr Smith gave him a lot of valuable advice on how to improve his writing.

Answer 1

2. that/which/不填；when 第一空先行词为the moment，在定语从句中作forget的宾语，要用that或which引导，也可以省略关系词；第二空用when引导表语从句，并在从句中作时间状语。