钢在拉拔时发生颈缩现象，断口呈现杯锥状，我们称之为（）
A.韧性断裂
B.晶间断裂
C.解理断裂
D.正断
参考答案：C
_____ the earth to be flat, many feared that Columbus would fall off the edge of the earth. [ ]
A. Having believed
B. Believing
C. Believed
D. Being believed
组成听性脑干反应的正波是（）。
A.3个
B.4个
C.5个
D.6个
E.7个
