The correct answer is D.  

Stroke is a major cause of disability and death in the United States.  High blood pressure (hypertension) is one of the most powerful modifiable (treatable) risk factors for ischemic and spontaneous hemorrhagic stroke, and it is very common.  

Answer a is incorrect because hyperglycemia (high blood sugar) is not the most powerful risk factor for stroke.  If caused by diabetes, high blood sugar is a risk factor for stroke.  Diabetes is often present with high blood pressure, high cholesterol, and obesity, so it may be associated with several risk factors for stroke.  But high blood sugar alone is not a specific risk factor for stroke.  

Answer b is incorrect because high blood potassium is not a risk factor for stroke.  

Answer c is incorrect because high blood sodium is not a risk factor for stroke.