请问It is a time 后面只能加when吗?that行吗?由the same 修饰的先行词在定语从句中,as和that都能做先行

It is a time 里面的a time是表示“一个时期/时代”的意思,从考点来分析,后面更多是接一个由when/in which/ during which引导的定语从句.如：It is a time when we communicate through cellhphones instead of lett...