II. Instrumental Variable 4. (Construction of instruments) Suppose Y7 - X;B + 6, where X, is 5 x 1 and all the variables in it are endogenous except the constant 1. We only have one instrument Zi. i) Suppose E(c:| Z,) = 0. Alice argues that she can construct infinitely many different instruments using Z, alone so that the model is still identified. Explain why that is possible. in) When Z, is a dummy variable, is Alice approach still valid