**Core Concept**
The underlying principle being tested is the pathophysiological mechanism of pruritus in primary biliary cirrhosis, which involves **cholestasis** and the accumulation of **bile salts**.

**Why the Correct Answer is Right**
Pruritus in primary biliary cirrhosis is primarily caused by the accumulation of **bile salts** in the skin, which stimulates nerve endings and causes itching. This occurs due to **cholestasis**, where bile flow is reduced or blocked, leading to a buildup of bile salts.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because while **lymphoma** can cause itching, it is not the primary cause in primary biliary cirrhosis.
**Option B:** Incorrect as **viral hepatitis** has a different pathophysiology.
**Option C:** Incorrect because **drug reactions** are not the primary cause of pruritus in primary biliary cirrhosis.
**Option D:**

**Clinical Pearl / High-Yield Fact**
A key point to remember is that **ursodeoxycholic acid** is often used to treat primary biliary cirrhosis and can help alleviate pruritus by improving bile flow.

**Correct Answer:** D. Bile salts.