a government gives its approval for the building of a private airport because the airport would be socially beneficial. in making its decision, it calculates private costs at $700 million, private benefits at $800 million and external costs at $200 million. what does this suggests must be true about the external benefits of this airport? 1. external benefits exceed $10 million, but less than $100 million. 2. there are no external benefits. 3. external benefits exceed external costs. 4. external benefits exceed $100 million. 5. external benefits equal private benefits. (mcq, choose only one answer)