18. One kind of tools which are in common use for daily maintenance works on theship is the one-piece with a U-shaped opening that grips two opposite faces of a boltor nut. This tool is often double-ended with different-sized opening at each end. Eachend of the tool is often oriented at an angle of around 15 degrees to the longitudinalaxis of the handle. Which tool is above description?
(A) Adjustable spanner
(B) Ring spanner
(C) Open-end spanner
(D) Hammer