几个从句的题~1.You can fly to London this afternoon_______you don'

几个从句的题~
1.You can fly to London this afternoon_______you don't mind changing plane for Paris.A provided B unless C except D so far as答案是A 这是什么意思,unless我觉得应该更合题意2._______the students were discussing the car accident,Benne put in that the road was icy.A Since B Where C While D As soon as答案是C while引导后面的时态不是应该和前面一样的吗?3.The situation today is obviously different from____it was about 30 years ago.A what B when C which D such答案是A 后面不是有30年吗? 怎么不用when?