**Core Concept**
The question pertains to the process of casting in dentistry, specifically the centrifugal casting technique used to create metal restorations. The size of the sprue is a critical factor in this process, as it affects the quality and accuracy of the final casting.

**Why the Correct Answer is Right**
The size of the sprue in centrifugal casting is determined by the metal of modulus (M.O.D.) of the casting. In the case of a bicuspid M.O.D. casting, the metal is typically invested in a crucible and then melted by a centrifugal casting machine. The size of the sprue is directly related to the metal's modulus of elasticity, which is a measure of its ability to resist deformation under stress. A smaller sprue size is required for a bicuspid M.O.D. casting because of its lower modulus of elasticity, which allows for more accurate and detailed reproduction of the casting's surface.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not take into account the specific characteristics of the bicuspid M.O.D. casting, such as its lower modulus of elasticity.
**Option B:** This option is incorrect because it suggests a larger sprue size, which would result in a less accurate and more distorted casting.
**Option C:** This option is incorrect because it implies a fixed sprue size that does not account for variations in the metal's modulus of elasticity.

**Clinical Pearl / High-Yield Fact**
When casting with centrifugal force, it's essential to consider the metal's modulus of elasticity to achieve accurate and detailed results. A smaller sprue size is typically required for bicuspid M.O.D. castings due to their lower modulus of elasticity.

**Correct Answer: C. 0.012 inches**