. It is argued that output may be endogenous. Four instrumental variables are proposed, initial initial level of real GDP , school : a measure of the population's educational attainment, inv average investment share of GDP, and poprate = average population growth rate. ll (a) Give an intuitive explanation as to Why output can be endogenous (3 marks) (13) Explain Why the proposed IVs can be valid. (6 marks, i.e., 2 marks for understanding of valid IVs and 1 mark for convincing story for each IV)