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.enlarge bit

B.casing bit

C.hole opener

D.casing opener

货币政策就是通过控制货币的需求量，使货币的需求量和供应量相适应，从而实现社会总需求和总供给的平衡。( )