1.Tom had opened the door _____ mary had time to knock.
A.until
B.beforeC.asD.although
2.It's high time you ______.
A.do you homework
B.would have done your homework
C.had done your homework D.did your homework
3.The bus wsa held up on way to the airport,otherwise I_____the plane.
A.must catchB.have caughtC.could have caughtD.ought to catch
4.Let's ____when the train will arrive.
A.discoverB.find C.find out D.look
5.If this continues to tske place at the present rate,____another fifty years,the world will be crowded with big ants.
A.at B.forC.inD.on
6.john will ___ Jack to be the general manager,for Jack is goning to channge his work.
A.take placeB.take the place ofC.take his placeD. take the place
1.bMary还没敲门，Tom就已经把们打开了，before表示顺序关系2.a现在正是做作业的时候，除了一般时态别的时态都不合适3.c这里用虚拟语气，只能选could have caught4.cfind out这里表示“查明”，discover（发现），find（寻找），look（看）都不合适5.cin表示将来一段时间内会发生6.b这里只有take the place of 后面能接名词...
