The correct answer is B) rudder. A "contra-guide" is a type of rudder, specifically a rudder that is designed to counteract the effects of a single screw propeller. The contra-guide rudder helps to compensate for the asymmetric thrust produced by a single-screw propeller, which can cause the vessel to yaw or deviate from its intended course. This type of rudder is commonly used on vessels with a single-screw propulsion system to improve maneuverability and directional stability. The other options are incorrect because they do not represent types of contra-guides. Cargo gear, bow thrusters, and steering engines are not related to the concept of a contra-guide rudder.