What Does the Depolarization of the Transverse Tubules (T ^-tubules)

What does the depolarization of the transverse tubules (T ^-tubules) promote?

A) release of acetylcholine from vesicles in the motor neuron into the synaptic cleft
B) binding of acetylcholine to ligand ^-gated sodium ion channels
C) entry of sodium ions into the muscle fiber through voltage ^-gated sodium ion channels
D) release of calcium from the sarcoplasmic reticulum