动力工具打磨的主要辅助材料是什么?()
A、砂磨片
B、碗型钢丝盘
C、榔头
参考答案:A, B
It was in the hall______ we usually have dinner______ we had a dancing party last night. [ ]
A. where; that
B. that; where
C. where; which
D. which; where
试述先天性肠闭锁和肠狭窄病理分类。