Which of These Statements Describes Twitch Summation

Which of these statements describes twitch summation

A) The muscle fibre is restimulated before the action potential has returned to resting potential.
B) The muscle fibre is restimulated before the filaments have completely returned to their resting position.
C) Stronger muscle contractions occur with stronger action potentials.
D) Weaker muscle contractions occur despite stronger action potentials.