从A、B、C、D四个选项中，选出可以填人空白处的最佳选项，并在答题卡上将该项涂黑。
21．—Oh, must you? Stay a bit longer. It has been such fun having you.
—Thanks anyway. I’ll get early start tomorrow.
A．/; the B．a; an C．/; an D．the; an
22．—Have you moved into the new house?
—No, the building is construction.
A．at B．under C．for D．in
23．— you like the car so much, why not drive it back?
—Well, I can’t afford car.
A．Now that; that big a B．If; such big a
C．When; so a big D．So long as; that a big
