**Core Concept**
Thromboprophylaxis refers to the use of medications to prevent the formation of blood clots, which can lead to conditions such as deep vein thrombosis (DVT) and pulmonary embolism (PE). Various classes of medications are used for thromboprophylaxis, including anticoagulants, antiplatelet agents, and fibrinolytic agents.

**Why the Correct Answer is Right**
Anticoagulants, such as heparin and warfarin, work by inhibiting the coagulation cascade, preventing the formation of thrombin and subsequent clot formation. Antiplatelet agents, like aspirin, prevent platelet activation and aggregation, thereby reducing the risk of clot formation. Fibrinolytic agents, like streptokinase, break down existing clots.

**Why Each Wrong Option is Incorrect**
* **Option A:** is actually used for thromboprophylaxis, as it is an anticoagulant that inhibits the coagulation cascade.
* **Option B:** is used for thromboprophylaxis, as it is an antiplatelet agent that prevents platelet activation and aggregation.
* **Option C:** is used for thromboprophylaxis, as it is a fibrinolytic agent that breaks down existing clots.

**Clinical Pearl / High-Yield Fact**
When choosing an anticoagulant for thromboprophylaxis, it is essential to consider the patient's renal function, as some anticoagulants, like warfarin, require dose adjustments in patients with renal impairment.

**Correct Answer:** D.