三道关于非谓语和虚拟语气的题.英语
1.Whyhasn‘thecome?_____ontime,wewouldhavetoputoffthetrip.
A.ifhedoesn'tcome
B.ifhewon'tcome
C.ifheshouldn'tcome
D.ifhehadn'tcome
2.Thestudenswillhavemorediscussionslikethisintheweeks______.
A.comingB.tocomeC.comeD.tobecoming
3.________halfwaythroughtheexercise,theteacherchangedhismindandcollectedallourpapers.
A.Whenonlybeing
B.Whenwewereonly
C.Beingonly
D.Havingbeen
能不能说下答案并告诉我其他选项错在哪,或用了什么语法搭配.