A deepwell pump is a type of（）.

A.join lines of equal size
B.form a temporary eye (loop) at the end of a line
C.be a stopper
D.keep a line from fraying

A.bight block
B.gin block
C.heel block
D.snatch block

A.when it is not under strain
B.if both ends are made fast
C.in an emergency
D.at no time