**Core Concept**
The question is testing the student's knowledge of macrophage function and its role in the central nervous system (CNS). Macrophages are a type of immune cell that play a crucial role in the clearance of pathogens, debris, and dead cells. In the CNS, macrophages are involved in maintaining immune homeostasis and preventing autoimmune responses.

**Why the Correct Answer is Right**
The correct answer is **D. Microglia**. Microglia are a subset of macrophages that are resident in the CNS. They are the primary immune cells of the brain and spinal cord, responsible for surveillance, phagocytosis, and antigen presentation. Microglia express specific receptors and markers that allow them to interact with neurons and other immune cells in the CNS.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because microglia are not the same as peritoneal macrophages, which are macrophages found in the peritoneal cavity.

**Option B:** This option is incorrect because astrocytes are a type of glial cell that provide support and maintenance functions in the CNS, but they are not macrophages.

**Option C:** This option is incorrect because oligodendrocytes are a type of glial cell responsible for myelination of neurons in the CNS, but they are not macrophages.

**Clinical Pearl / High-Yield Fact**
Microglia play a critical role in neuroinflammatory diseases, such as multiple sclerosis and Alzheimer's disease. Activated microglia can release cytokines and chemokines that exacerbate inflammation and tissue damage.

**Correct Answer: D. Microglia**