A、All professional athletes. B、All stars. C、A few stars. D、International tennis stars. C文章中提到有些运动员能挣到一百万美元，但这只是一部分运动员。故选C。

The word "sports" first meant something that people did in their free time. Later it often meant hunting wild animals and birds. About 100 years ago the word was first used for organized games. This is the usual meaning of the word today. People spend a lot of their spare time playing football, basketball, tennis and many other sports. Such people play because they want to. A few people are paid for the sport they play and they are called "professional athletes", or "pros". They may only be pros for only a few years, but during that time the best ones can earn a lot of money. For example, a professional football player in America earns more than $100, 000 a year. The stars earn a lot more. Some international golf and tennis pros can make more than a million dollars a year. Of course, only a few pros can earn much money. But perhaps the most surprising thing about pros and money is this: the stars can earn more money from advertising than from sports. An advertisement for sports equipment  does not simply say "Buy our things." It says "Buy the same shirt and shoes as the pros have." Famous pros can even advertise things like watches and food, They allow companies to use their names or photographers and they are paid for this usage. Sports are. no longer just something  for people’s spare time.