Look ! Someone is celebrating his birthday .   This must be his 21st birthday . No doubt about it .   Why ? Do you know that guy ?   No . Well , in America , 21 is the age when you're allowed to drink . So , many guys celebrate it in bars .   That's interesting . But it would be really expensive , I suppose . Just think about all the drinks .   No . If it's your birthday , then you don't need to pay a cent . Just blow out the candles and open the gifts . That makes the birthday a special day . Your friends will take care of everything .   Wow . That's wonderful .   What about in China ? What'd you do to celebrate your birthday ? 