**Core Concept**
Warfarin is an anticoagulant that works by inhibiting the synthesis of vitamin K-dependent clotting factors in the liver. An International Normalized Ratio (INR) measures the time it takes for blood to clot and is used to monitor warfarin therapy. A therapeutic INR range is typically between 2.0 and 3.0, but the target INR may vary depending on the indication for anticoagulation.

**Why the Correct Answer is Right**
The correct answer is **Option C:** 1.5 to 2.0. The INR is used to assess the effectiveness of warfarin therapy and to guide dosage adjustments. A preoperative INR of 1.5 to 2.0 indicates that the patient is adequately anticoagulated and at a lower risk of thromboembolic complications during surgery. This range is considered safe for elective surgery, as it minimizes the risk of bleeding while still providing effective anticoagulation.

**Why Each Wrong Option is Incorrect**
* **Option A:** 3.0 is too high and may increase the risk of bleeding during surgery.

**Clinical Pearl / High-Yield Fact**
It's essential to note that the target INR range may vary depending on the indication for anticoagulation, such as atrial fibrillation or deep vein thrombosis. Always consult the patient's medical chart and consult with the patient's physician to determine the optimal INR range for their specific condition.

**Correct Answer: C. 1.5 to 2.0**