## Core Concept
The movement of fluid across capillary walls is primarily governed by the forces described by the Starling equation. These forces include hydrostatic pressure and oncotic pressure, which together determine the net movement of fluid between the capillary lumen and the interstitial space.

## Why the Correct Answer is Right
The correct answer involves two key pressures: hydrostatic pressure and oncotic pressure. **Hydrostatic pressure**, the pressure exerted by blood within the capillary, pushes fluid out of the capillary and into the interstitial space. **Oncotic pressure**, primarily due to albumin in the blood, pulls fluid back into the capillary. The balance between these pressures determines whether fluid is filtered out of the capillary (net outward movement) or absorbed into it (net inward movement). The Starling equation is given by: Net filtration pressure = (Hydrostatic pressure in capillary - Hydrostatic pressure in interstitial space) - (Oncotic pressure in capillary - Oncotic pressure in interstitial space).

## Why Each Wrong Option is Incorrect
- **Option A:** This option is incomplete as it does not specify the types of pressures involved in capillary fluid dynamics.
- **Option B:** Similarly, this option lacks specificity regarding the pressures that influence fluid movement across capillary walls.
- **Option D:** This option might include incorrect or irrelevant pressures not directly related to the primary forces governing fluid movement across capillaries.

## Clinical Pearl / High-Yield Fact
A key clinical point to remember is that edema occurs when the balance of Starling forces shifts towards increased fluid movement out of capillaries and into the interstitial space. This can happen with increased hydrostatic pressure (e.g., heart failure), decreased oncotic pressure (e.g., nephrotic syndrome), lymphatic obstruction, or increased capillary permeability.

## Correct Answer: C.