应该是 If my birthday by solar calendar is on a weekday when/on which I have to work 因为A weekday is any of the days of the week except Saturday and Sunday.my birthday bysolar calendar is on a weekday on which I have to work, 这句这样对吗？ 那不就是有两个on了吗？第一个 on 是介词短语作表语 第二个on which 引导的是定语从句 修饰 第一个on 后面的名词 没有什么不妥