**Core Concept**
Normal prothrombin time (PT) is a measure of the extrinsic and common coagulation pathways, reflecting the integrity of the liver's synthetic function and the efficiency of the coagulation cascade. It is an essential parameter in assessing hemostasis and bleeding disorders. The normal range of PT varies among laboratories but generally falls between 11-14 seconds.

**Why the Correct Answer is Right**
The correct answer is based on the standard reference range for PT. This range is influenced by the presence of clotting factors II, VII, X, and fibrinogen, which are produced by the liver. The extrinsic pathway, initiated by tissue factor, converges with the common pathway, where factors X and V contribute to the formation of thrombin and fibrin. A normal PT indicates that the coagulation cascade is functioning properly, with all necessary factors present in adequate amounts.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not provide a numerical value, making it impossible to determine if it's correct or not.
**Option B:** This option is incorrect because it is lower than the normal range, suggesting a coagulopathy or liver dysfunction.
**Option C:** This option is incorrect because it is higher than the normal range, indicating a possible coagulation disorder or liver dysfunction.

**Clinical Pearl / High-Yield Fact**
A prolonged PT is often seen in patients with liver disease, vitamin K deficiency, or warfarin therapy. It's essential to note that PT is not a sensitive marker for coagulopathy, and a normal PT does not exclude the presence of a bleeding disorder.

**Correct Answer: C. 15-20 seconds**