**Core Concept**
The extrinsic and common coagulation pathways are critical components of the hemostatic process, working together to prevent excessive bleeding. The extrinsic pathway is activated by tissue trauma, leading to the formation of thrombin and subsequent clot formation. The common pathway involves the conversion of prothrombin to thrombin, which then catalyzes the conversion of fibrinogen to fibrin.

**Why the Correct Answer is Right**
The correct answer tests the extrinsic and common coagulation pathways by assessing the ability of tissue factor to activate factor VII, leading to the formation of factor VIIa-tissue factor complex. This complex then activates factor IX and factor X, which enter the common pathway. The common pathway involves the conversion of prothrombin to thrombin by factor Xa and factor Va, resulting in the formation of fibrin from fibrinogen. This process is crucial for the formation of a stable blood clot.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not specifically test the extrinsic and common coagulation pathways. The activated partial thromboplastin time (APTT) test primarily assesses the intrinsic and common coagulation pathways.
* **Option B:** This option is incorrect because it does not specifically test the extrinsic coagulation pathway. The prothrombin time (PT) test primarily assesses the extrinsic and common coagulation pathways, but it does not specifically test the extrinsic pathway.
* **Option C:** This option is incorrect because it does not specifically test the common coagulation pathway. The reptilase time test assesses the conversion of fibrinogen to fibrin, but it does not specifically test the common pathway.

**Clinical Pearl / High-Yield Fact**
The extrinsic and common coagulation pathways are critical for the formation of a stable blood clot. A deficiency in any of the factors involved in these pathways can lead to bleeding disorders such as hemophilia A and hemophilia B.

**Correct Answer: B. PT test. It tests extrinsic and common coagulation pathway.**