Growing up on her own

WORLD No 2 tennis player Jelena Jankovic from Serbia (塞尔维亚) has won her second title of the year. She became champion of the China Open on September 28.
Jankovic first practiced tennis when she was nine years old. After six months Jankovic played her first match.
It was the national championship for kids up to 10 years old. She came to the semi-finals (半决赛).
When she was 11, she won a national championship for girls up to 12 years old. In order to continue her career, Jelena left Serbia and went to the United States.
At that time, she didn’t speak any English. And her family did not come with her. It was a hard time.
“I did not know what I needed to do when I was going to school. I could not do my homework. When you have a difficulty, there is nobody to help you. So, you learn it the hard way,” Jelena said.
However, it was a good learning experience for Jelena. “It makes me more independent (独立的) and stronger as a person. I know how to do everything by myself so I don’t have to depend on (依赖) my parents or somebody else to do it for me,” she said.
In the US, Jelena received better conditions for practice and development of her game. In 2000, she became a professional (职业选手) and has been shining on the tennis court ever since.
根据上面短文的内容回答问题    
1. Where is Jelena Jankovic from?
2. What is Jelena Jankovic’s job?
3. Why did she leave for the United States?
4. When did she become a professional?
5. What do you think of her hard time in the United States?