悬吊式顶棚的顶棚龙骨具体分为哪几类？
参考答案：
龙骨的类型有U形龙骨、T形铝合金龙骨、T形镀锌铁烤漆龙骨、嵌入式金属龙骨等。
-- What’s the matter with you?
---____ the window, my finger was cut unexpectedly.
A．Cleaning
B．To clean
C．While cleaning
D．While I was cleaning
( )是专门用来开挖竖井或斜井的大型钻井。
A．天井钻B．独臂钻C．盾钻D．TBm
