高中英语现在完成进行时单选题

—I'm sure Andrew will win the first prize in the final.
—I think so.He ________ for it for months.

A．is preparing	B．was preparing
C．had been preparing	D．has been preparing

—Why，Jack，you look so tired!
—Well，I ________ the house and I must finish the work tomorrow.

A．was painting	B．will be painting
C．have painted	D．have been painting

Tom ________ in the library every night over the last three months.(2011·北京)

A．works	B．worked
C．has been working	D．had been working