Immediately following the arrival of the stimulus at a skeletal muscle cell there is a short period called the period during which the neurotransmitter is released by exocytosis, diffuses across the synaptic cleft, and binds to its receptors.
a) contraction
b) relaxation
c) latent
d) refractory

latent.

Explanation:

When a muscle gets a stimulus, there is a lag in the start of a contraction. This delay in muscle contraction after the application of stimulus is called the latent period. During the latent period, the calcium ions are released from the sarcoplasmic reticulum and the action potential sweeps over sarcolemma as a neurotransmitter is released in synaptic cleft and bind to its receptors present on the postsynaptic membrane.

The latent period is followed by a contraction period. The latent period mostly lasts for 2 milliseconds. The contraction period is marked by binding of calcium ions to troponin and exposure of myosin binding site on actin and formation of the cross bridge. This is followed by a relaxation period.