7322
He comes to know the source of the poisonous air in the environment , and he comes in contract some Aliens who tell him that if he destroys it , all the survivors die but have found an alternative , a device that will slowly clear the poisonous air .
 None
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 None