Explanation: The grid capacitor in a three-circuit regenerative receiver is crucial for grid-leak detection. It works with the grid-leak resistor to develop a self-bias on the grid, allowing the tube to detect the amplitude-modulated signal and facilitating regeneration. If this capacitor is shorted: 1. **It effectively shorts the grid to the cathode (or ground via the grid-leak resistor if present and not also shorted), shunting the RF signal.** This prevents proper signal application to the grid and destroys the grid-leak detection mechanism, rendering the receiver mostly or completely inoperative (A). Regeneration, which relies on proper tube gain and feedback, would also cease. 2. **Without the proper grid bias developed by the capacitor, the tube's operating point is severely altered.** While the primary grid-leak detection is gone, the tube still acts as a non-linear device. It may perform some crude rectification of strong signals, essentially operating as a poor plate detector. This would result in considerably reduced sensitivity and volume compared to a properly functioning grid-leak detector (C). Therefore, both outcomes are possible, making D the correct answer.