1.---Shall we go outing this weekend?

1.---Shall we go outing this weekend?
---Oh,with all this work( ),I don't know if I'll have time to go out
A to do B doing C done D do
2.Working in an air-conditioned office,you can hardly imagine what a hard time the peasants have ( )rice.
A to growing B to grow C grown D growing
3.( ) the temperature falling so rapidly,we could't go on with the experiment.
A since B with C as D for
4.The Whites are( )holiday .But I don't know where they have gone( )their holidays.
A in;for B on;for C for;in D at; on
5.He has three brothers,( )is a doctor.
A all of them B all of whom C none of them D none of whom(这道题的答案是D,为什么C ）