Which of the following statements best describes fused tetanus?

A brief and single contraction-relaxation cycle of muscle fiber in response to a single stimulus.

An increase in muscle force resulting from repeated stimuli arriving at the muscle fiber before the previous twitch has completely relaxed.

A smooth and continuous contraction resulting from the rapid stimulation of the muscle, without any relaxation in between.

An increase in muscle force resulting from the activation of additional motor units within a muscle.