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The conditions for clearance of the alliance were that British Airways and American drop 168 slots at London Heathrow airport , the busiest in Europe .
 organization: British Airways; organization: American; location: London Heathrow; location: Europe
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: location, else, organization, person 
Text: {0} 
Answer:
 organization: British Airways; organization: American; location: London Heathrow; location: Europe