## **Core Concept**
The question tests the understanding of coagulation pathways and their relationship with Partial Thromboplastin Time (PTT) and Prothrombin Time (PT). PT and PTT are crucial tests used to evaluate the extrinsic and intrinsic coagulation pathways, respectively.

## **Why the Correct Answer is Right**
Option suggests a condition affecting the extrinsic pathway of coagulation, which primarily involves factors VII, X, V, II (prothrombin), and fibrinogen. A prolongation of PT with a normal PTT indicates a problem in this pathway. Vitamin K deficiency or warfarin therapy affects the production of vitamin K-dependent clotting factors (II, VII, IX, and X), leading to a prolongation of PT. This is because factor VII is exclusively part of the extrinsic pathway.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option would likely affect both PT and PTT since it involves factors present in both the intrinsic and extrinsic pathways or the common pathway.
- **Option B:** This condition affects the intrinsic pathway, which would primarily prolong the PTT, not the PT.
- **Option D:** This option might affect both PT and PTT or only PTT, depending on the specific deficiency or condition, but it does not characteristically present with a prolonged PT and normal PTT.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that isolated prolongation of PT suggests a problem with the extrinsic pathway, which could be due to deficiencies in factors VII, X, V, II, or fibrinogen. Vitamin K deficiency and warfarin therapy are classic causes of such a pattern.

## **Correct Answer: C.**