## Core Concept
The question tests the understanding of neurotransmitters and their roles in the nervous system. Neurotransmitters can be broadly classified into excitatory and inhibitory types based on their effect on the postsynaptic neuron. Excitatory neurotransmitters depolarize the postsynaptic neuron, increasing the likelihood of an action potential.

## Why the Correct Answer is Right
Glutamate is the primary excitatory neurotransmitter in the central nervous system (CNS). It acts on various receptors, including **NMDA**, **AMPA**, and **kainate receptors**, which are ligand-gated ion channels. When glutamate binds to these receptors, it leads to an influx of positively charged ions (such as sodium and calcium) into the postsynaptic neuron, causing depolarization. This depolarization can lead to an excitatory postsynaptic potential (EPSP) and increases the likelihood of generating an action potential.

## Why Each Wrong Option is Incorrect
- **Option A:** GABA (gamma-aminobutyric acid) is the primary inhibitory neurotransmitter in the CNS. It acts on GABA receptors, which are ligand-gated ion channels or G protein-coupled receptors, leading to hyperpolarization or reduced excitability of the postsynaptic neuron. Therefore, it is incorrect as an excitatory neurotransmitter.
- **Option B:** Glycine is another inhibitory neurotransmitter, primarily in the spinal cord and brainstem. It acts on glycine receptors, which are ligand-gated chloride channels, causing an influx of chloride ions into the neuron, leading to hyperpolarization. Thus, it is not an excitatory neurotransmitter.
- **Option D:** Acetylcholine can act as both an excitatory and inhibitory neurotransmitter, depending on the type of receptor it binds to (muscarinic or nicotinic receptors). However, in the context of this question and considering the primary excitatory neurotransmitter, glutamate is more universally recognized for its excitatory role.

## Clinical Pearl / High-Yield Fact
A key point to remember is that **glutamate** is the most abundant excitatory neurotransmitter in the vertebrate nervous system. Dysregulation of glutamatergic transmission has been implicated in various neurological disorders, including Alzheimer's disease, Parkinson's disease, and epilepsy.

## Correct Answer: C. Glutamate