In the Experiment in Figure , the Motor Neuron of a Muscle

In the experiment in Figure , the motor neuron of a muscle expressed the P2X₂ transgene and the response in the muscle was recorded. Why did application of ATP activate the muscle? Figure

A) Addition of ATP activated of the P2X₂ channel which directly increased transmitter release by moving vesicles to the presynaptic membrane.
B) Addition of ATP resulted in opening of the P2X₂ channel and an influx of sodium, which activated the motor neuron, releasing neurotransmitter and activation of the muscle.
C) Addition of the resulted in activation of the P2X₂ protein, a G protein coupled receptor. Once activated the receptor increased the probability of neurotransmitter release and activated the muscle.
D) Addition of ATP resulted in activation of the ATP receptor, a G protein coupled receptor. Once activated, this G protein indirectly activated P2X₂, which increased the probability of neurotransmitter release from the motor neuron and activated the muscle.