It's that time of the yea—graduation. The end of school year is nearly in sight, and it's an especially big deal if you're finishing high school or college.One amazing (令人惊叹的) 16-year-old Florida girl, Grace Bush, graduated from both high school and college this week! She actually got her college diploma (毕业证书) before her high school diploma. How'd she do that?"Hard work and dedication (专心致志）, " she told a local TV news station, " have made me succeed in doing high school and college at the same time. " She started taking college courses when she was just 13. She would often get up at 5:30 a.m. and not finish until after 11 p. m.Doing both at once is a huge achievement, but it has also helped her family save money. She's one of the 9 children, all home-schooled until the age of 13. Her father is a math professor while her mother is a part-time history teacher in a high school. Grace Bush has earned her college degree in law, with a near perfect GPA of 3.8 and she hopes to become a lawyer one day, although her parents expect her to teach at university. By the way, she also plays basketball in her college team in her spare time.Which of the following is the key to Grace's success?（）。