Muscle Fibers Show a Range of Responses to Different Levels

Multiple Choice

Muscle fibers show a range of responses to different levels of stimulation because

A) each muscle fiber contraction is "all or none."
B) the availability of Ca²⁺ sets an upper limit to the strength of the contraction.
C) a new contraction can occur only after the resting condition is reached.
D) following stimulation, the fiber stays contracted.
E) individual twitches in the same fiber can summate.