**Core Concept**
Anticholinergic agents are a class of medications that block the action of acetylcholine, a neurotransmitter involved in various physiological functions. They are often used to treat conditions such as Parkinson's disease, peptic ulcers, and asthma. The tertiary amine structure refers to a specific chemical configuration of the compound.

**Why the Correct Answer is Right**
Tertiary amines have a quaternary ammonium group that is not ionized at physiological pH, which allows them to penetrate the blood-brain barrier and exert central anticholinergic effects. One of the most well-known tertiary amine anticholinergics is trihexyphenidyl, which is used to treat Parkinson's disease and drug-induced parkinsonism. The tertiary amine structure is responsible for its ability to cross the blood-brain barrier and exert its effects on the central nervous system.

**Why Each Wrong Option is Incorrect**
**Option A:** Atropine is a tertiary amine anticholinergic, but it is not the only one. However, the question asks for an example, and atropine is a well-known one.
**Option B:** Diphenhydramine is a first-generation antihistamine that also has anticholinergic effects, but it is not a tertiary amine.
**Option C:** Benztropine is a tertiary amine anticholinergic, but it is not as well-known as trihexyphenidyl.

**Clinical Pearl / High-Yield Fact**
When choosing an anticholinergic agent, it's essential to consider the specific indication and the potential for central versus peripheral effects. Tertiary amines like trihexyphenidyl are more likely to cross the blood-brain barrier and exert central effects.

**Correct Answer:** C. Benztropine.