**Core Concept**
Cerebral infarction, also known as ischemic stroke, occurs when a blood vessel supplying blood to the brain is obstructed, leading to a lack of oxygen and nutrients to the affected area. This results in cell death and tissue damage. The common causes of cerebral infarction involve atherosclerosis, hypertension, and cardiac embolism.

**Why the Correct Answer is Right**
The correct answer involves the pathophysiology of cerebral infarction, specifically the role of atherosclerosis in causing large artery occlusions. Atherosclerosis is the buildup of plaque in the arterial walls, leading to narrowing and eventual occlusion of the lumen. This reduces blood flow to the brain, resulting in ischemia and infarction. The other options, such as hypertension, cardiac embolism, and small vessel disease, are also contributing factors but are not the most common cause.

**Why Each Wrong Option is Incorrect**
**Option A:** Hypertension is a significant risk factor for cerebral infarction, but it is not the most common cause. It contributes to atherosclerosis and small vessel disease, which can lead to infarction.
**Option B:** Cardiac embolism is a common cause of cerebral infarction, particularly in the context of atrial fibrillation. However, it is not the most common cause overall.
**Option C:** Small vessel disease is a common cause of lacunar infarcts, but it is not the most common cause of cerebral infarction overall.

**Clinical Pearl / High-Yield Fact**
Atherosclerosis is a systemic process that affects multiple vascular beds, including the coronary, cerebral, and peripheral vasculature. This highlights the importance of managing risk factors for atherosclerosis, such as hypertension, hyperlipidemia, and smoking, to prevent cardiovascular and cerebrovascular disease.

**Correct Answer: A. Atherosclerosis**