英语语法:虚拟语气I didn't know his telephone number.____ it,I ____ then.

问题描述:

英语语法:虚拟语气I didn't know his telephone number.____ it,I ____ then.
C.If I knew; would ring him up
D.Had I known; would have rung him up
请问C错在哪?是因为那个then吗?then在这里是作时间状语吗?

是判断是对过去的虚拟呀 then的意思就是那时.对过去的虚拟.从句过去完成,主句would/should/could/might have done