—I've been trying to            him for twenty minutes. Why won't he stop crying?

—Ah, Can't you see he is cutting onions? [ ]

A.cheer on

B.cheer up

C.cheered on

D.cheered up

水利工程由于其建筑物特有的结构特征，一般都需耗用大量的建筑材料，如混凝土重力坝其材料费占工程直接成本的（）。

A.40～50%

B.50～60%

C.60～70%

D.70～80%