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:       There will be another sandstorm here tomorrow .  
 Person2:It's the fourth one this year . Isn't it horrible .  
 Person1:        Yes . We should plant more trees and grass to stop the sand from spreading .  
 Person2:It may take many years for the trees to grow . I hope people will stop cutting down trees .  
 Person1:        But we need the wood .  
 Person2:But we can't destroy our forests to get the wood . 

informal