请问这几道英语题目请帮我指出选择题答案的原因（道理）,1.The man you want to see has arr

请问这几道英语题目
请帮我指出选择题答案的原因（道理）,
1.The man you want to see has arrived.______he come at once?
填 Shall
2.Come what ____,we are not going to make any concessions to his unreasonable demands.
填 may .
3.We ought to go there by air,_____?
填 shouldn't we
4.On no account_____our friends.
填 must we betray .
5._____that Tom did it,what harm is there?
填 Granted .
以上5题希望您来为我们讲解一下,