The ladder shall（）.

A. be secured in a position so that it rests firmly against the ship's side from which the discharge operations are carried out
B. have at least two replacement steps which are secured in position by a method different from that used in the original construction
C. have battens made of hardwood，or other material of equivalent properties，in one piece and not less than 1.80metres long provided at such intervals as will prevent the pilot ladder from twisting
D. have steps made of softwood，or other material of equivalent properties，made in one piece free of knots，having an efficient slip surface