**Core Concept**
Hodgkin's disease, also known as Hodgkin lymphoma, is a type of lymphoma characterized by the presence of distinctive cells called Reed-Sternberg cells. These cells are a hallmark of the disease and play a crucial role in its diagnosis and pathogenesis.

**Why the Correct Answer is Right**
Reed-Sternberg cells are large, abnormal lymphocytes that are typically multinucleated and contain distinctive nucleoli. They are thought to arise from germinal center B cells and are characterized by their expression of CD30 and CD15 surface antigens. The presence of Reed-Sternberg cells is a diagnostic criterion for Hodgkin lymphoma, and their identification is essential for distinguishing this disease from other types of lymphoma.

**Why Each Wrong Option is Incorrect**
* **Option A:** Incorrect because Reed-Sternberg cells are not characterized by the presence of a single large nucleolus, but rather multiple nucleoli. Additionally, they are not typically found in non-Hodgkin lymphomas.
* **Option B:** Incorrect because lymphoblasts are a type of cell found in acute lymphoblastic leukemia (ALL), not Hodgkin lymphoma. They are smaller and more immature than Reed-Sternberg cells.
* **Option C:** Incorrect because plasma cells are a type of mature B cell found in conditions such as multiple myeloma, not Hodgkin lymphoma. They are distinct from Reed-Sternberg cells in terms of their morphology and immunophenotype.

**Clinical Pearl / High-Yield Fact**
Reed-Sternberg cells are often surrounded by a halo of lymphocytes, which can make them appear as "owl eyes" under the microscope. This characteristic appearance is a key diagnostic feature of Hodgkin lymphoma.

**Correct Answer: C. Reed-Sternberg cells.**