--- Listen! David is talking happily with his mother in the next room.　--- It ______ be his mother. She has gone to Yunnan to be a volunteer doctor.

I told Sally how to get here, but perhaps I ______for her.

He _____ be really difficult at times even though he ,generally speaking, is a nice person. 

—Must I return the book this week?— No, you ____. You can ____ it for 20 days.

My pen doesn’t work well. Could I borrow _____, John?