**Core Concept:** Secondary hypertension is a form of hypertension (high blood pressure) that develops due to an underlying cause. It is distinguished from primary hypertension, which has no identifiable cause. Understanding the causes of secondary hypertension is essential for appropriate diagnosis and treatment.

**Why the Correct Answer is Right:**

Correct answer C, "Venous congestion," refers to an increase in blood volume that leads to elevated blood pressure. This condition can result from blockage or obstruction in the renal veins, causing venous hypertension. Renal veins reflux back to the kidneys and returning blood to the heart. When these veins become obstructed or damaged, blood accumulates in the kidneys, increasing pressure on the nephrons and ultimately leading to hypertension.

**Why Each Wrong Option is Incorrect:**

A. Angiotensin-converting enzyme (ACE) inhibitors are used to treat hypertension, not cause it. These medications are not part of the list of correct answers.

B. Angiotensin II receptor blockers (ARBs) are another class of antihypertensive drugs. They also do not cause hypertension but rather help manage it.

D. Calcium channel blockers are a type of antihypertensive medication. Like ACE inhibitors and ARBs, they are used to treat hypertension, not cause it.

**Clinical Pearl / High-Yield Fact:**

Understanding the different types of hypertension (primary and secondary) is critical for accurate diagnosis and treatment planning. Secondary hypertension can be caused by various underlying conditions, such as renal vein obstructions. This distinction helps prevent unnecessary treatment with antihypertensive medications and ensures appropriate management of the underlying cause.