Explanation: Grid-leak bias is a self-biasing technique commonly used in vacuum tube transmitters. When the grid is driven positive relative to the cathode by an RF input signal, it acts like a diode and draws current (grid current). This current charges a small capacitor in the grid circuit, which then discharges through a grid-leak resistor, creating a negative DC bias voltage across the resistor. **B) The value of grid leak resistance and duration of time the grid current is flowing:** The *grid leak resistance* is crucial as it determines the magnitude of the voltage drop for a given grid current, thereby setting the negative bias. The *duration of time the grid current is flowing* influences the average charge built up on the grid capacitor and consequently the stable bias level, as it's part of the RC time constant. **C) Internal resistance of the tube between the grid and cathode:** This inherent characteristic of the vacuum tube dictates *how much* grid current flows when the grid is driven positive. This current is fundamental, as it's what flows through the grid leak resistor to generate the bias voltage. Therefore, both the external grid leak resistance (B) and the tube's internal grid-cathode characteristics (C) are critical for establishing and maintaining the correct operating bias. Option A is incorrect, as "grid leak anode to grid" is not a relevant concept for this biasing method.