**Core Concept**
Acute inflammation is a complex, protective response of the body to injury or infection, characterized by increased blood flow, vascular permeability, and the movement of leukocytes into affected tissues. This process involves various cell types, chemical mediators, and molecular pathways that work together to restore tissue integrity and eliminate pathogens.

**Why the Correct Answer is Right**
The correct answer is **A. Exudative**. Exudative inflammation is the most common type of acute inflammation, characterized by the migration of leukocytes and the exudation of fluid, proteins, and enzymes into the affected tissue space. This process is facilitated by the increased permeability of blood vessels, which allows for the entry of plasma proteins and leukocytes into the interstitial space. The exudation of fluid and proteins leads to the formation of exudates, which can accumulate in the affected tissue and contribute to the inflammatory response.

**Why Each Wrong Option is Incorrect**
**Option B:** Suppurative inflammation is a specific type of acute inflammation characterized by the production of pus, which is a mixture of leukocytes, bacteria, and dead tissue. While suppurative inflammation is a common complication of acute inflammation, it is not the most common variety.

**Option C:** Fibrinous inflammation is a type of acute inflammation characterized by the deposition of fibrin, a protein that forms a network of fibers in the affected tissue. While fibrinous inflammation can occur in various tissues, it is not the most common variety of acute inflammation.

**Option D:** Serous inflammation is a type of acute inflammation characterized by the exudation of clear fluid, such as serum or plasma, into the affected tissue space. While serous inflammation can occur in some tissues, it is not the most common variety of acute inflammation.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the type of inflammation can vary depending on the underlying cause, location, and duration of the inflammatory response. For example, a bacterial infection may lead to suppurative inflammation, while a chemical injury may cause fibrinous inflammation.

**Correct Answer: A. Exudative inflammation**