Final answer:
The percentage of people in the United States with at least one major risk factor for coronary heart disease by age 20 is not specified, but the risk is significant and lifestyle changes are recommended to reduce it.
Step-by-step explanation:
The student is asking about the percentage of people in the United States who have at least one major risk factor for coronary heart disease by age 20.
According to the Centers for Disease Control and Prevention (CDC), factors such as age, genetics, and various lifestyle factors like smoking, diabetes, obesity, and physical inactivity contribute to the risk of developing heart disease. Although specific statistics for those aged 20 are not provided, we can infer that heart disease risk factors are prevalent among younger individuals, and preventative measures encourage adopting healthier lifestyle choices early in life to reduce these risks.
Furthermore, the average disease rate of 33.9 percent in the United States suggests that the prevalence of these risk factors is significant within the population, though we cannot define the exact percentage in the provided options without more specific data for the age group in question.