**Core Concept**
Lardaceous spleen, a condition characterized by the deposition of amyloid, is a type of splenic amyloidosis. This condition leads to the enlargement and hardening of the spleen due to the accumulation of amyloid fibrils in the splenic tissue.

**Why the Correct Answer is Right**
The correct answer is **A. Sinusoids of red pulp** because amyloid deposition in the spleen primarily affects the red pulp, which is composed of venous sinuses and splenic cords. The amyloid fibrils accumulate in the walls of these sinusoids, leading to their thickening and obliteration, thereby impairing the spleen's filtering function. This process ultimately results in the characteristic enlargement and hardening of the spleen.

**Why Each Wrong Option is Incorrect**
**Option B:** Amyloid deposition is not typically associated with the white pulp of the spleen, which is primarily composed of lymphoid cells and follicles.
**Option C:** The pencillary artery is not a primary site for amyloid deposition in the spleen. While amyloidosis can affect various vessels, the pencillary artery is not a characteristic location for amyloid accumulation.
**Option D:** Splenic trabeculae, which are fibrous connective tissue strands supporting the splenic architecture, are not the primary site for amyloid deposition in lardaceous spleen.

**Clinical Pearl / High-Yield Fact**
In amyloidosis, the deposition of amyloid fibrils can lead to the disruption of normal tissue architecture and function, resulting in a range of clinical manifestations, including splenomegaly (enlarged spleen), hepatomegaly (enlarged liver), and nephrotic syndrome (kidney damage). It is essential to recognize the characteristic features of amyloidosis and its effects on various organs to make an accurate diagnosis and develop an effective treatment plan.

**✓ Correct Answer: A. Sinusoids of red pulp**