_____ is necessary for us to tell him about the result.
The roads are crowded _____ walking is quicker than driving.
---Did your car break down again this morning? ---Yes.That’s ____ I was late.
You must do your homework now; you ___ basketball all the evening.
As I will be away for at least a year, I’d appreciate ____ from you now and then, _____ me how everyone is getting along.
I’d like ___ on a trip to Tibet while he prefers ___ to Guilin.