Question

Oct. 1, 1949 is the day ________ I will never forget.

1. A.
   when
2. B.
   in which
3. C.
   that
4. D.
   on which

Answer 1

C
该句定语从句的先行词为时间，但根据句意分析，从句中forget需要宾语，表示我永远都不会忘记“那个日子”，所以引导词应用关系代词that/which或省略不用。