The correct answer is D. A "left-handed" propeller is a propeller which rotates in the counter-clockwise direction when viewed from astern. This is correct because in marine engineering, the direction of rotation of a propeller is determined from the perspective of an observer looking at the propeller from the stern (aft) of the vessel. A "left-handed" propeller rotates in the counter-clockwise direction when viewed from this aft-facing perspective. The other options are incorrect because they do not accurately describe the definition of a "left-handed" propeller. A propeller's location on the vessel (port or starboard side) or its ability to rotate in either direction does not determine whether it is considered "left-handed" or "right-handed".