plss help

1. a) Explain how barriers to entry can result in oligopoly. (20 marks) b) Using a diagram, explain why changes in marginal cost may not result in price changes in oligopoly. (30 marks) 2. a) Explain, using a diagram, why production of a good that causes pollution might be higher than is socially optimal. (30 marks) b) Explain how a government could act in this case to ensure the socially optimal outcome. (10 marks) c) Briefly explain two other reasons why governments might want to intervene in markets. (10 marks) 3. a) Briefly explain three main objectives of macroeconomic policy. (10 marks) b) State the three main types of unemployment and explain why each type occurs. (25 marks) c) Explain why a country might not want an unemployment rate of zero. (15 marks)