since when ,since then的区别（在线等）he came back from abroad in 1998,since when,he has been doing his business.这一句中为什么用since when 却不能用since then ,

分类: 作业答案 • 2021-12-19 11:45:33

问题描述：

since when ,since then的区别（在线等）
he came back from abroad in 1998,since when,he has been doing his business.这一句中为什么用since when 却不能用since then ,

答

这是个以when引导的定语从句,不能用then的,因为since when前面是逗号