**Core Concept**
Actinomycetes are a group of bacteria that are commonly found in the human oral cavity, particularly in the cervico-facial region. They are known for their characteristic branching filaments and are often associated with various infections, including actinomycosis.

**Why the Correct Answer is Right**
The correct answer, **D. Pencillin is used in treatment for 6 weeks**, is incorrect because actinomycosis is typically treated with a prolonged course of penicillin, but the duration is usually 2-3 weeks, not 6 weeks. This is because actinomycetes produce penicillinase, which can break down penicillin, making it less effective. Therefore, a longer treatment course is often necessary to ensure complete eradication of the infection.

**Why Each Wrong Option is Incorrect**
* **Option A:** Actinomycetes are actually acid-fast, as they contain mycolic acids in their cell walls, which give them this characteristic staining property.
* **Option B:** While actinomycosis is indeed most commonly found in the cervico-facial region, this option is not false about actinomycetes.
* **Option C:** Actinomycetes are not obligate anaerobes, as they can grow in both aerobic and anaerobic conditions, although they are often found in environments with low oxygen levels.

**Clinical Pearl / High-Yield Fact**
Actinomycosis is a chronic infection that can mimic other conditions, such as malignancy or abscesses, making it essential to consider this diagnosis in patients with persistent or recurrent infections in the cervico-facial region.

**✓ Correct Answer: D. Pencillin is used in treatment for 6 weeks**