A single heavy wire made up for the topping lift is called a（）.

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

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A “figure eight” knot is used to（）.

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

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