**Core Concept**
The phenomenon of rosette formation with sheep red blood cells (RBCs) is a diagnostic tool used to identify T lymphocytes. This process is based on the specific interaction between T cells and sheep RBCs, which is mediated by a protein called CD2 on the surface of T cells.

**Why the Correct Answer is Right**
T lymphocytes, also known as T cells, are a type of white blood cell that plays a central role in cell-mediated immunity. The rosette formation with sheep RBCs is a characteristic feature of T cells, which is used as a marker to identify them in the laboratory. This process is thought to be mediated by the CD2 protein, which is present on the surface of T cells and binds to the surface of sheep RBCs. The binding of CD2 to sheep RBCs leads to the formation of a rosette, which is a cluster of T cells surrounding a sheep RBC.

**Why Each Wrong Option is Incorrect**
**Option A:** Erythrocytes (red blood cells) do not have the CD2 protein on their surface and therefore do not form rosettes with sheep RBCs.

**Option B:** Monocytes are a type of white blood cell that does not express the CD2 protein and therefore does not form rosettes with sheep RBCs.

**Option C:** Neutrophils are a type of white blood cell that does not express the CD2 protein and therefore does not form rosettes with sheep RBCs.

**Clinical Pearl / High-Yield Fact**
The rosette formation with sheep RBCs is a classic diagnostic tool used to identify T lymphocytes in the laboratory. This technique is particularly useful in the diagnosis of T cell lymphomas and leukemias.

**Correct Answer: C. T lymphocytes.**