A、4 years. B、5 years. C、8 years. D、At least 9 years. D综合推断题，文章开始就提到，在美国，任何想从医的人都必须经过4年普通大学和4年医学院的学习，还有1至5年在医院的实习期，由此推断，他们在正式成为医生

Men and women in the United States who want to become doctors usually attend four years of college or university; next they study for four years in a medical school. After that they work in hospitals as medical residents or doctors in training for one to five years. Some people study and work for as many as 13 years before they begin their lives as doctors.
    During their university years, people who want to become doctors study science intensively. They must study biology, chemistry and other sciences. If they do not, they may have to return to college for more education in science before trying to enter medical school.
T    here are 125 medical schools in the United States. It is difficult to gain entrance to them. Those who do the best in their studies have a greater chance of entering medical school. Each student also must pass a national examination to enter a medical school. Those who get top scores have the best chance of being accepted. Most people who want to study medicine seek to enter a number of medical schools. This increases their chances of being accepted by one. In 1999, almost 47,000 people competed for about 17,000 openings in medical schools.