He could have come to help us ,but_____.a.he didn't b.he hasn't c.he hadn't d.he can't为什么选a不选b如果后面写反义疑问句是不是用didn't he?

He could have come to help us ,but_____.a.he didn't b.he hasn't c.he hadn't d.he can't为什么选a不选b如果后面写反义疑问句是不是用didn't he? --I haven't seen Mike for some time,what---to him?--He's got crazy and has ---hospitalA,should have happened,come inB,can have happened,ended inC,could have happened,come inD,must have happened,likely选哪个?为什么? Bob could have seen the famous star _yesterday morning.A did he come B if he came C had he comeD if he should come i don't think he could have done better than that,()?A.do i B.don't i C.could he D.couldn't he __ he fail to come over,what could we do without him?For you see,we don't have the key to the lab!A If B should C Whether D unless come down to my levelI could see your compassion.and then you came down to my level I was the one who was nervous he said.Idon't normally have someone look me in the eye You don't have to wait any more,he won't come back I don’t think he could have done such a stupid thing last night,____?A.do I B.could he C.did he D.has he could you come over to my house .sorry ,i ---.i have to do my homework first括号里是填could还是 couln't还是 can还是 can't I'm surprised that he should have attended the meeting but he didn't come up还有attended the meeting but he didn't come 1-16why hasn't he come?( )on time,we will have to put off the trip.1.if he doesn't come2.if he won't come3.if he shouldn't come4.if he hadn't come He said Jack ( ) come to the party,but I don't think soA could B might C need D will he needn't have come to see me off in person,____?a.did he b.need he c.has he d.needn't he选哪一个?急要! Don't touch the sleeping tiger ,If he woke up,he____youA would come toB would come atC would have come to wardD will come to I don't think he could have done such a stupid thing last night,__ A.could he B had he Cdid he这里could不是情态动词,have不是助动词吗?为什么要用did?（答案选C） Oh,you have come back .I____I could see you again in such a short time.A didn't expect Don't leave until he _____ back tomorrowA have come B comes C will come D is coming要解释 last night Tom didn't come,but he ought to have怎样解析?