## Core Concept
Hodgkin's lymphoma (HL) and non-Hodgkin's lymphoma (NHL) are two distinct types of lymphomas, which are cancers of the lymphatic system. The key to differentiating between them lies in their histopathological characteristics. Specifically, the presence of **Reed-Sternberg cells** is a hallmark feature.

## Why the Correct Answer is Right
The correct answer, , is right because **Reed-Sternberg cells** are characteristic and diagnostic of Hodgkin's lymphoma. These are large, abnormal lymphocytes that contain more than one nucleus, each with a distinctive "owl-eye" appearance due to large nucleoli. The presence of these cells is a critical distinguishing feature from non-Hodgkin's lymphomas, which do not contain Reed-Sternberg cells.

## Why Each Wrong Option is Incorrect
* **Option A:** This option is incorrect because while the **age distribution** and **clinical presentation** can sometimes overlap between Hodgkin's and non-Hodgkin's lymphomas, they do not reliably differentiate between the two.
* **Option B:** This option is incorrect because **B symptoms** (fever, night sweats, and weight loss) can occur in both Hodgkin's and non-Hodgkin's lymphomas, making them not specific enough to differentiate between the two.
* **Option C:** This option is incorrect because **cellular origin** from B cells or T cells can be seen in both types of lymphomas, and while certain subtypes of NHL are more commonly associated with specific cell types, this does not universally differentiate HL from NHL.

## Clinical Pearl / High-Yield Fact
A key clinical pearl is that **Reed-Sternberg cells are pathognomonic** for Hodgkin's lymphoma. Their identification is crucial for the diagnosis, and their absence rules out Hodgkin's lymphoma. This is a high-yield fact for any medical student or postgraduate to remember.

## Correct Answer Line
**Correct Answer: D. Reed-Sternberg cells.**