**Core Concept**
The process of acute inflammation involves a complex series of events, including the recruitment of immune cells, the release of chemical mediators, and changes in blood vessel permeability. Vasodilation and increased vascular permeability are critical steps in this process, allowing for the influx of immune cells and the delivery of oxygen and nutrients to the affected area.

**Why the Correct Answer is Right**
Vasodilation refers to the widening of blood vessels, which increases blood flow to the affected area. This is mediated by the release of chemical mediators such as histamine, bradykinin, and prostaglandins, which stimulate the relaxation of smooth muscle cells in the blood vessel walls. Increased vascular permeability allows for the leakage of fluid and proteins from the blood vessels into the interstitial space, creating edema and facilitating the migration of immune cells into the affected area. This process is essential for the initiation of the inflammatory response and the delivery of immune cells to the site of injury or infection.

**Why Each Wrong Option is Incorrect**
**Option A:** Vasoconstriction, on the other hand, is a response that occurs in the early stages of inflammation, but it is short-lived and is quickly replaced by vasodilation. Vasoconstriction would actually decrease blood flow to the affected area, which would impede the delivery of oxygen and nutrients.

**Option B:** Vascular stasis refers to the slowing or cessation of blood flow, which can occur in the later stages of inflammation due to the release of chemical mediators that stimulate the contraction of smooth muscle cells in the blood vessel walls. However, this is not an important step in the initiation of acute inflammation.

**Option D:** Margination of leukocytes is an important step in the inflammatory response, but it occurs after vasodilation and increased vascular permeability have taken place. Margination refers to the movement of leukocytes from the bloodstream into the vicinity of the affected area, where they can migrate through the endothelium and into the interstitial space.

**Clinical Pearl / High-Yield Fact**
The release of chemical mediators such as histamine and bradykinin during acute inflammation can lead to the development of systemic effects, including hypotension and tachycardia. This is why antihistamines and beta-blockers are sometimes used to treat severe allergic reactions.

**✓ Correct Answer: C. Vasodilation and increased vascular permeability**