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:       Mr.Ben , What do you think of the book ?  
 Person2:It's an excellent one . I like it very much .  
 Person1:        Why ?  
 Person2:It includes a lot of useful words and phrases .  
 Person1:        I agree with you . 

informal