If Na⁺ Cannot Enter a Muscle Fiber in Response to a Stimulus

Multiple Choice

If Na⁺ cannot enter a muscle fiber in response to a stimulus,

A) contraction cannot occur.
B) relaxation cannot occur.
C) Na⁺ will be released from the sarcoplasmic reticulum instead.
D) the active sites are left exposed.
E) the action potential travels into the muscle anyway.