Take the linear instrumental variables equation YI = Z, + Y22 + e with Ele | Z] = 0 where both X and Z are scalar 1 1. (a) Can the coefficients (B1, f2) be estimated by 2SLS using Z as an instrument for Y2? Why or why not? (b) Can the coefficients (Br, 2) be estimated by 2SLS using Z and Z? as instruments? (c) For the 2SLS estimator suggested in (b), what is the implicit exclusion restriction? (d) In (b) what is the implicit assumption about instrument relevance? [Hint: Write down the implied reduced form equation for Y2.1 (e) In a generic application would you be comfortable with the assumptions in (c) and (d)