Which training method is another variation of variable pace method?

The correct option is Fartlek method.

Fartlek training, which translates to "speed play" in Swedish, is a training method that combines elements of continuous training and interval training.
During a Fartlek session, an athlete varies their running pace dynamically and continuously throughout the run. Instead of following a strictly structured set of intervals and recovery periods, the change in speed is often unstructured and determined by the terrain, feelings of the athlete, or self-selection.

Because the core mechanism of this training involves constantly changing and adjusting the running speed throughout a continuous workout, it is considered another variation of the variable pace method.