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:       Hello . Can I talk to David ? 
 Person2:One second , please . ( a few seconds later , the receiver comes back and says ) Hello ? 
 Person1:        Yes . 
 Person2:I ’ m sorry . David is out to lunch right now . 
 Person1:        Okay . I ’ m his wife . Could you tell him to call me back when he returns ? 
 Person2:Sure . Does he know where to call you ? 
 Person1:        Oh , thanks . Please tell him to call my cell-phone number . 
 Person2:Ok , I will . 
 Person1:        Thank you very much . 
 Person2:No problem . 

informal