钢结构加工制作中的关键步骤是( )。
A．焊接
B．制孔
C．煨弯
D．滚圆
参考答案：A
Miss Jones _______ music at Bardon School for five years when she was abroad and now she is an actress.
A．taught
B．has taught
C．had taught
D．has been teaching
耐火等级为三级的一般民用建筑的层数不应超过（）。
A.八层
B.七层
C.六层
D.五层
