**Core Concept**
The question is testing the knowledge of the autonomic nervous system, specifically the neurotransmitters released by nerve fibers innervating sweat glands. The autonomic nervous system is a branch of the nervous system that controls involuntary functions, such as sweating, heart rate, and digestion.

**Why the Correct Answer is Right**
Sweat glands are innervated by cholinergic nerve fibers, which release acetylcholine (ACh) as their neurotransmitter. ACh binds to muscarinic receptors on the sweat gland, stimulating the gland to release sweat. This is an example of a parasympathetic nervous system (PNS) response, as the PNS is responsible for promoting rest and relaxation, including the release of sweat to cool the body.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not specify the neurotransmitter released by nerve fibers innervating sweat glands. While dopamine is an important neurotransmitter, it is not the primary neurotransmitter released by sweat gland innervation.
* **Option B:** This option is incorrect because it mentions norepinephrine, which is a neurotransmitter released by sympathetic nervous system (SNS) fibers, not parasympathetic fibers. The SNS is responsible for promoting the "fight or flight" response, which is opposite to the PNS response of sweating to cool the body.
* **Option C:** This option is incorrect because it mentions serotonin, which is a neurotransmitter involved in mood regulation and other functions, but not directly related to sweat gland innervation.

**Clinical Pearl / High-Yield Fact**
Remember that cholinergic nerve fibers, which release acetylcholine, are responsible for innervating sweat glands and promoting the release of sweat. This is an important aspect of the autonomic nervous system and can be a key factor in diagnosing conditions such as hyperhidrosis (excessive sweating).

**Correct Answer: A. Acetylcholine**