Definition: You are given a conversation between two people. 'Person1:' and 'Person2:' are used to separate their respective dialogues. You are required to assign a label 'formal' if there is an absence of emotion and a presence of questions anywhere within the conversation. If such pattern is not found assign the label 'informal'.
Input:  Person1:       Look ! Someone is celebrating his birthday .  
 Person2:This must be his 21st birthday . No doubt about it .  
 Person1:        Why ? Do you know that guy ?  
 Person2:No . Well , in America , 21 is the age when you're allowed to drink . So , many guys celebrate it in bars .  
 Person1:        That's interesting . But it would be really expensive , I suppose . Just think about all the drinks .  
 Person2: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 .  
 Person1:        Wow . That's wonderful .  
 Person2:What about in China ? What'd you do to celebrate your birthday ?  
 Person1:        Nowadays , it's no difference from America . But in old times , we have traditional ways to celebrate it . 

informal