A device used to enlarge the size of an existing bore hole, having teeth arranged on its outside circumference to cut the formation as it rotates is a(n) ______.
A.enlarger bit
B.casing bit
C.hole opener
D.casing opener
正确答案：C
扩孔器是一个被用来扩大镗孔尺寸的设备其周边镶有锯齿以在转动时切割成型
