The search was________ when night came，even though the child had not been found.

A．approved

B．acquired

C．achieved

D．abandoned

古罗马人善用（）结构，它是由放射形排开的楔形拱石之间相互产生张力撑开拱面。

A.混凝土

B.山墙

C.柱式

D.拱券