B. a slot is cut partly in middle of nut and then slot reduced by tightening a screw

C. through slots are made at top and a cotter-pin is passed through these and a hole in the bolt, and cotter spitted and bent in reverse direction at other end

D. a hard fiber or nylon cotter is recessed in the nut and becomes threaded as the nut is screwed on the bolt causing a tight grip

E. none of the above