Question

That is the day( ) i‘ll never forget. A.which. B.on which. C.in which. D when

Answer 1

此题答案为A。这是一个考查定语从句中关系代词和关系副词用法的题目，此句的先行词是一个表时间的名词，通常，修饰表时间的名词的定语从句的引导词根据情况选用when/on which/in which/ during which...，如：
I'll never forget the day when /on which I met her for the first time.
句中的when/ on which 引导定语从句，并做从句I met her for the first time的时间状语，状语应用副词，在定语从句中做状语应用关系副词。
而提问中的 That is the day which I will never forget.中的which引导定语从句，并做从句I will never forget的宾语，宾语应用代词，在定语从句中做宾语语应用关系代词。

Answer 2

A Forget 后面缺宾语

追问

为什么选A D不对么

追答

D不对，选WHEN必须后面不缺宾语，FORGET及物动词需宾语

追问

哦