Expert  say that students usually need eight to ten hours' sleep at night, but most Chinese students do not get enough sleep. Some Chinese parents are usually glad to see their children studying late. They will think their children work very hard, but not all parents are happy about this. Once a mother told us tat every morning her 10-year-old boy put up one finger  with his eyes still closed, begging  for one more minute to sleep. Like thousands of students " early birds" in China, he has to get up before six every morning. A report shows that without a good night's sleep, students seem to be weaker  than they should be. Many students have fallen asleep during class at one time or another. Too much homework is not the only reason why students stay up late. Some watch TV or play the computer games late into the night. Experts have ever said that the students should develop good study habits. So some clever students never study last, they are able to work well in class. In this passage "early birds" means "persons who   _  "
get up early get up late sleep less don't want to sleep