1）The peerson you-Beijing is quite suitable.

C have go have sb. do sth. ”叫/让/使某人做某事“
这里原来的句子是： You have the person go to Beijing. The person is quite suitable.
have sb. do sth.=let sb. do sth.= make sb. do sth.=get sb. to do sth. ”叫/让/使某人做某事“
其中get一定要加上不定式符号to 其他都不带to
B to help I did all I could=I did all I could do (to do sth.)
这里是不定式表示目的.could 的后面本身省略了do.
C has happened do you suppose是插入语 和句子的时态无关.
其他的还有What do you think/feel/believe 等等.
上文的for a long time决定下文用现在完成时.
确信!
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