Why Do Individual Muscle Twitches Have to Be Added Together

Multiple Choice

Why do individual muscle twitches have to be added together, as in summation or tetanus?

A) Only added twitches produce any muscle contraction: A fiber undergoing a muscle twitch does not contract at all.
B) There has to be a critical mass of muscle twitches for calcium to be released into the muscle cell.
C) Not enough acetylcholine will be produced for contraction without multiple twitches.
D) Multiple twitches add up to an increase in muscle fiber tension, which increases the strength of the muscle.
E) Not enough ATP is generated by one muscle twitch.