**Core Concept:** Streptokinase is a fibrinolytic agent used to dissolve blood clots, including those in deep vein thrombosis (DVT). Hematemesis refers to vomiting blood, which can be a complication due to the breakdown of blood vessels during clot dissolution.

**Why the Correct Answer is Right:**
In this scenario, the correct answer is **Option D: **Oral N-acetylcysteine** (NAC). NAC is an antioxidant and mucolytic agent, which can protect the gastrointestinal mucosa from damage caused by streptokinase and similar fibrinolytics. It can prevent or reduce the risk of mucosal injuries and bleeding events like hematemesis.

**Why Each Wrong Option is Incorrect:**
A. **Aspirin:** While aspirin is an antiplatelet agent, it is not indicated for preventing mucosal damage caused by fibrinolytics like streptokinase.
B. **Sucralfate:** Sucralfate is a protective agent for the gastrointestinal tract, but it is not specific to fibrinolytics and may not be as effective as NAC in preventing or reducing mucosal injuries.
C. **H2-receptor antagonists (e.g., ranitidine):** These are antacids used to reduce stomach acid secretion, which is unrelated to the mucosal protection needed in this context.

**Clinical Pearl:**
Hematemesis in a patient receiving streptokinase or similar fibrinolytics should prompt consideration of mucosal protection. Oral N-acetylcysteine (NAC) is a more appropriate choice compared to other medications like aspirin, sucralfate, or H2-receptor antagonists like ranitidine. NAC specifically targets the mucosal protection needed to prevent or reduce mucosal injuries and bleeding events like hematemesis.

**Correct Answer:** Option D: Oral N-acetylcysteine (NAC)