一些英语时态选择题

一些英语时态选择题
1)after I had walked for six hours,( )
A;i had been tired out B:i 'll be tired out
C:i was tired out D;i would have been tired out
2)the students( )busily when Miss Green went to get a book she( )in the office.
A;had written,left B;were writing,has left
C;had written,had left D;were writing,had left
3)"we could have walked to the station as it was so near."
"yes.a taxi( )at all neccessary."
A;wasn't B.hadn't been C;wouldn't be Dwon't be
4)he'll be an astronaut by the time he( )thirty
A;is B;had been C;will be D:is going to be
5)we were all surprised when h made it clear that he( )office soon
A;leaves B;would leave C;left D;had left