**Core Concept**
The concept of center of resistance (CR) in dental anatomy is crucial for understanding the mechanics of dental prosthetics and orthodontics. The CR is the point where the forces applied to a tooth are most effectively resisted, and its location depends on the height of the alveolar bone surrounding the tooth.

**Why the Correct Answer is Right**
As the alveolar bone height moves apically (towards the apex of the tooth), the center of resistance also shifts apically. This is because the alveolar bone acts as a fulcrum, and as the bone height decreases, the CR moves towards the apex. This is due to the changed lever arm and the altered distribution of the tooth's volume. The CR's apical movement is essential in orthodontic tooth movement and dental prosthetic design, as it affects the forces required to move or stabilize a tooth.

**Why Each Wrong Option is Incorrect**
**Option B:** The CR does not move coronally (towards the crown of the tooth) as the alveolar bone height decreases. Instead, it moves in the opposite direction.

**Option C:** The CR does not move mesially (towards the mesial aspect of the tooth) as the alveolar bone height decreases. The CR's movement is primarily apical.

**Option D:** The CR does not move to infinity as the alveolar bone height decreases. While the CR's location is affected by the alveolar bone height, it remains finite and is determined by the tooth's geometry.

**Clinical Pearl / High-Yield Fact**
Remember that the center of resistance is a critical concept in dental anatomy, and its location affects the forces required for tooth movement and stabilization. Understanding the CR's behavior as alveolar bone height changes is essential for designing effective dental prosthetics and orthodontic treatments.

**✓ Correct Answer: A. Apically. The center of resistance moves apically as the alveolar bone height decreases.**