**Core Concept**
Hodgkin's lymphoma, also known as Hodgkin's disease, is a type of lymphoma characterized by the presence of distinctive cells called Reed-Sternberg cells. The diagnosis of Hodgkin's lymphoma is confirmed by histopathological examination of lymph node biopsy.

**Why the Correct Answer is Right**
The correct answer involves the identification of Reed-Sternberg cells and their variants, which are characteristic of Hodgkin's lymphoma. These cells are typically large, multinucleated, and have a distinctive "owl's eye" appearance due to the presence of a large nucleolus surrounded by a clear halo. The presence of Reed-Sternberg cells is a hallmark of Hodgkin's lymphoma and is considered diagnostic.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the diagnosis of Hodgkin's lymphoma is not confirmed by clinical presentation alone, although certain symptoms such as fever, night sweats, and weight loss may be present.
**Option B:** This option is incorrect because the diagnosis of Hodgkin's lymphoma is not confirmed by imaging studies such as CT or PET scans, although these may be used to stage the disease.
**Option C:** This option is incorrect because the diagnosis of Hodgkin's lymphoma is not confirmed by laboratory tests such as blood counts or tumor markers, although these may be used to monitor the disease.

**Clinical Pearl / High-Yield Fact**
A key feature of Reed-Sternberg cells is their presence in the lymph node sinuses, rather than within the lymphoid follicles. This is a useful clue for pathologists to confirm the diagnosis of Hodgkin's lymphoma.

**Correct Answer: D. Histopathological examination of lymph node biopsy.**