**Core Concept**
Chromatography is a laboratory technique used to separate a mixture of substances based on their interactions with a stationary phase and a mobile phase. The technique relies on the differential movement of substances through a matrix, allowing for the separation and identification of individual components.

**Why the Correct Answer is Right**
In chromatography, mass movements of the substances are primarily due to differences in their affinity for the stationary phase and the mobile phase. The stationary phase, which can be a solid or liquid, attracts substances through various interactions such as adsorption, absorption, or partitioning. The mobile phase, which can be a gas or liquid, carries the substances through the matrix, allowing for their separation based on their relative affinities for the stationary phase. The movement of substances is influenced by factors such as their molecular weight, polarity, and charge.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not accurately describe the primary mechanism driving mass movements in chromatography.
**Option B:** This option is incorrect because it is too vague and does not specifically address the interactions between substances and the chromatography matrix.
**Option C:** This option is incorrect because it is unrelated to the fundamental principles of chromatography.

**Clinical Pearl / High-Yield Fact**
A useful mnemonic to recall the key components of chromatography is "SPM": Stationary Phase, Mobile Phase, and Matrix. Understanding these components is crucial for selecting the appropriate chromatography technique for a given analysis.

**Correct Answer:** D. Differences in affinity for the stationary and mobile phases.