The answer is b. electrical signals and chemical neurotransmitters.
Electric signals include action potential. When neurons hit threshold and action potential is triggered, the Na+ channels open and Na+ ions enter the neuron. After the depolarization of membrane, Na+ channels inactivate. Consequently, the action potential is generated.
When an action potential reaches presynaptic terminal on a neuron, it will induce a release of neurotransmitters from the neuron. Neurotransmitters pass through the synaptic cleft and bind to the receptor on a postsynaptic neuron.
