Isaac Observed a Sample of Motor Units in Which Single

Multiple Choice

 Isaac observed a sample of motor units in which single neurons innervated fibers of the same type. This led Isaac to conclude that

A) neural input probably determines the identity of muscle fibers as slow- or fast-twitch.
B) the organism that supplied the samples had probably suffered a spinal cord injury.
C) the organism that supplied the samples was very old.
D) his sample was not representative, and he needed to obtain more samples before reaching a conclusion.