For each of the following, identify whether the statement is true, false or uncertain and justify your answer (you may use a graph, algebra or words, but you must fully explain your answer.)
a) If everyone has the same marginal rate of substitution, then the allocation is Pareto efficient.
b) If a policy change increases social welfare, then it must be a Pareto improvement.
c) In a two-person economy, it is not Pareto efficient to give all the goods to one person.