The correct answer is D: All these choices are correct. Good ways to guard against electrical shock at your station include: using three-wire cords and plugs, connecting all AC equipment to a common safety ground, and installing mechanical interlocks in high-voltage circuits. All three are important safety measures. Three-wire cords provide grounding, common grounding ensures all equipment is at the same potential, and interlocks prevent access to high voltage when equipment is opened. For amateur radio operators, multiple layers of protection are essential for electrical safety.