**Core Concept**
Rivaroxaban is a direct oral anticoagulant (DOAC) that inhibits factor Xa, a key enzyme in the coagulation cascade. It is a synthetic, small molecule that selectively binds to and inhibits factor Xa, preventing the conversion of prothrombin to thrombin.

**Why the Correct Answer is Right**
Rivaroxaban works by selectively binding to the active site of factor Xa, thereby preventing the formation of thrombin and subsequent clot formation. This results in a decrease in thrombin generation and a subsequent decrease in clot formation. Rivaroxaban's mechanism of action is similar to that of heparin, but it is a direct inhibitor of factor Xa, whereas heparin requires the presence of antithrombin for its anticoagulant effect.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it is not a specific category of anticoagulants. While rivaroxaban is indeed an oral anticoagulant, this option does not provide enough information to accurately categorize it.
**Option B:** This option is incorrect because it is a category of anticoagulants that includes warfarin, which works by inhibiting vitamin K-dependent clotting factors, not factor Xa.
**Option C:** This option is incorrect because it is a category of anticoagulants that includes heparin, which works by activating antithrombin and inhibiting thrombin and factor Xa, but is not a direct inhibitor of factor Xa like rivaroxaban.

**Clinical Pearl / High-Yield Fact**
It is essential to note that DOACs, including rivaroxaban, have a rapid onset and offset of action, which can affect their dosing and monitoring. The most common side effects of rivaroxaban include bleeding, which can be serious and even life-threatening.

**Correct Answer: C. Factor Xa inhibitors. Direct oral anticoagulants.**