**Core Concept**
The question tests the understanding of **actinomycosis**, a chronic bacterial infection caused by *Actinomyces* species, and the composition of **sulphur granules**, which are a hallmark of this disease. Sulphur granules are aggregates of the bacteria that form in tissues.

**Why the Correct Answer is Right**
Sulphur granules in actinomycosis consist of **filaments of Actinomyces**, which are Gram-positive, anaerobic bacteria. These filaments are the key component of the granules, which are essentially colonies of the bacteria.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the composition of sulphur granules is not primarily made of other materials.
**Option B:** Similarly, this option is incorrect as it does not accurately describe the bacterial nature of the granules.
**Option D:** This option is also incorrect because it does not correctly identify the bacterial filaments as the main component.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that actinomycosis often presents with **chronic abscesses** or **masses**, and the presence of sulphur granules in drainage or tissue is diagnostic.

**Correct Answer:** D. filaments of Actinomyces