型钢塔架由于用工字钢、槽钢、角钢制成，其断面一般为( )。

A．三角形空间桁架结构

B．四方形空间桁架结构

C．六边形空间桁架结构

D．梯形空间桁架结构

The actress who had been thought highly of       to be a great disappointment.

A．turned down

B．turning in

C．turned out

D．turning up