为什么这句定语从句中不能用that要用when?October1,1949 is the day when the People's * was founded.

问题描述:

为什么这句定语从句中不能用that要用when?
October1,1949 is the day when the People's * was founded.

因为在定语从句(the people's * was founded)中,缺少的是时间状语,全句应该是the people's * was founded on october 1,1949.