单项选择题 A device fitted over the discharge opening on a relief valve consisting of one or two woven wire fabrics is called a（）.

单项选择题 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)（）.

单项选择题 A Doppler log in the bottom return mode indicates the（）.