**Core Concept**
Selegiline is a selective, irreversible inhibitor of monoamine oxidase B (MAO-B), an enzyme involved in the breakdown of dopamine, norepinephrine, and epinephrine. By inhibiting MAO-B, selegiline increases the levels of these neurotransmitters in the brain, which can lead to improved mood and cognitive function.

**Why the Correct Answer is Right**
Selegiline works by binding covalently to the active site of MAO-B, thereby preventing the breakdown of dopamine and increasing its availability for neurotransmission. This mechanism of action is distinct from other antidepressants that may increase dopamine levels through mechanisms such as reuptake inhibition or receptor agonism. The selective inhibition of MAO-B by selegiline also reduces the risk of side effects associated with non-selective MAO inhibitors, such as hypertensive crises.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because selegiline is not a serotonin reuptake inhibitor, which is a different class of antidepressant that targets the serotonin system.

**Option B:** This option is incorrect because selegiline is not a direct-acting dopamine agonist, which would stimulate dopamine receptors directly rather than increasing dopamine levels through inhibition of MAO-B.

**Option C:** This option is incorrect because selegiline is not a direct-acting norepinephrine agonist, which would stimulate norepinephrine receptors directly rather than increasing norepinephrine levels through inhibition of MAO-B.

**Clinical Pearl / High-Yield Fact**
Selegiline has a unique property known as "pro-drug" activity, where it is metabolized to its active form, L-amphetamine, which contributes to its antidepressant and anti-parkinsonian effects.

**Correct Answer: C. Selegiline is a selective, irreversible inhibitor of monoamine oxidase B (MAO-B).**