Final answer:
About 68 million Americans suffer from hypertension, which makes the estimated number of people with hypertension in the United States closest to 70 million; therefore, the correct answer is D. 70 million.
Step-by-step explanation:
Chronically elevated blood pressure, known clinically as hypertension, affects tens of millions of Americans. The condition is often asymptomatic, making it a 'silent killer' and leading to serious health consequences such as heart attacks, strokes, and other cardiovascular diseases if left untreated. According to the information provided, about 68 million Americans currently suffer from hypertension, meaning the correct answer to the student's question is D. 70 million.