The bus came sfter I --------- for about half an hour
Ahad been waited Bhave waitedCwas waiting Dhad been waiting
2、Don't disturb me,I-----letters all morning and have written two so far
AwriteBhave writtenCwas writingDhave been writing
3、The building of the lab -----before the end of this term
Amust have completedBmust have been completed
Cmust be completed Dmust complete
4、What were you doing when I phoned you?
I had just finished my work and-------to take a bath
Astarting Bto startChave startedDwas starting
5、Have you seen the doctor yet?
No, but -----------(这一题我是选B,为什么不能选B,D和B有什么区别?)
AI goB I'm going to see C I go to see D I'm going to
请在给出解答的同时也给出详细解析,谢谢,我会追加悬赏的~~~