A seaman needs to join two lines of unequal diameter under moderate strain. Which knot or bend is most appropriate for this task?

Why C is correct

NAVEDTRA 14067 §3-2 states the sheet (becket) bend joins two lines, especially of unequal size, and holds better than a square knot. The square knot is suited only for lines of equal size under light duty. The bowline forms an eye, not a joining bend, and the clove hitch secures a line to a spar.