Explanation:

- The amplification factor is a key parameter of a triode, which indicates how effectively the device amplifies a signal.

- Option 1: Plate resistance

- Plate resistance influences how the current flows through the triode.

- Changes in plate resistance can affect the amplification factor.

- Option 2: Plate voltage

- It impacts the operating point of the triode but not directly the amplification factor.

- Option 3: Filament voltage

- Affects the emissions of electrons, altering triode efficiency, not directly amplification.

- Option 4: Plate current

- It's linked to operating conditions, but again, indirectly affects amplification.

Correct Answer: Option 1 - Plate resistance