1）there comes a time in every man's life (when he has to think)?
用which he needs 不行 因为意思不对
如果 用which 则代替先行词 a time在定从中 作宾语
本句应该 用when =during which 引导定从 在从句中作状语 意思才通顺.
2）yet no firm evidence had come to light （that）the men arrested were actually responsible.用which不可以 因为这不是定语从句 而是名词性从句 作同位语 是同位语从句 补充说明 evidence
3)do you like the book your father gave you
very much.it is exactly( the one) i want.
这个地方的the one是表语 后面是省略that的定语从句
如果用that 或者which则是表语从句 意思不通 如果是定从则缺先行词.