The correct answer is A: Near the center of the vertical radiator. The most efficient location for a loading coil on an electrically short whip is near the center of the vertical radiator. This location minimizes losses and maximizes efficiency. Loading coils have resistance (loss). Placing the coil at the center (where current is maximum) means the high current flows through the coil, but the coil's resistance causes losses. However, placing it at the center is actually more efficient than at the base or top because it allows better current distribution. The center location provides a good compromise - it's not at the high-current base (which would cause more loss) but allows the antenna to work more efficiently than if the coil were at the top. The exact optimal location depends on the specific design, but center is generally best.