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.be a stopper
B.shorten a line
C.join lines of equal size
D.keep a line from passing through a sheave

A.ISSA stores
B.IMPA stores
C.common marine stores
D.a reference to be studied

A.ISSA stores are numbered in six digits
B.IMPA stores are numbered in six digits
C.IMPA stores are numbered in seven digits
D.both ISSA and IMPA stores are numbered in unique six digits