单元检测(五)一、单项填空(共15小题;每小题1分,满分15分)请从A、B、C、D四个选项中,选出可以填入空白处的最佳选项。1.—I’ll call you ________ I arrive in Shenzhen.—Thanks,and good luck.A.while B.untilC.as D.once2.Three fifths of the land ________ covered by trees in this area.A.is B.are C.has D.have3.The students listened carefully to the teacher with their eyes ________ the blackboard.A.f