**Core Concept**
In orthodontics, anchorage is a fundamental concept used to control tooth movement while minimizing unwanted side effects. Anchorage is achieved through various mechanisms, including expansion, retraction, and rotation. The type of anchorage used depends on the desired movement and the available space.

**Why the Correct Answer is Right**
Reciprocal anchorage refers to a type of anchorage where two or more units work together to achieve a desired movement. In this case, an expansion alliance made with an expansion screw involves two or more screws that work together to expand the dental arch. This type of anchorage is reciprocal because the force generated by one screw is balanced by the opposing force from the other screw, resulting in a stable and controlled expansion. The expansion screw works by applying a continuous force to the dental arch, which is then distributed across the teeth and surrounding bone. This distribution of force is critical in preventing unwanted side effects, such as root resorption or tooth movement.

**Why Each Wrong Option is Incorrect**
**Option A:** Simple anchorage refers to a type of anchorage where a single unit is used to achieve a desired movement. This does not apply to an expansion alliance made with two or more screws.
**Option C:** Multiple anchorage refers to a type of anchorage where multiple units are used to achieve a desired movement, but the movement is not reciprocal. This is not the case with an expansion alliance made with two or more screws.
**Option D:** Reinforced anchorage refers to a type of anchorage where additional support is provided to a single unit to achieve a desired movement. This is not relevant to an expansion alliance made with two or more screws.

**Clinical Pearl / High-Yield Fact**
When using expansion screws, it's essential to remember that the force generated by the screws should be evenly distributed across the dental arch to prevent unwanted side effects. A common mistake is to apply too much force, which can lead to root resorption or tooth movement.

**✓ Correct Answer: B. Reciprocal anchorage**