搭设脚手架人员必须戴安全帽、但不必系安全带、可以偶尔穿皮鞋。（）
参考答案：错
A modern city has been built _____ a very small village was many years ago.
A．what
B．where
C．that
D．in which
简述什么样类型的零件加工首选数控机床。
