Suppose the Phillips curve in an economy is Π t
​
=Π t
e
​
−0.5(u−u N
​
). The Central Bank aims to increase annual nominal money supply at a rate of 3%, which is equal to the growth rate of the price level of aggregate output. If the rate of unemployment in this period is 3%, last period inflation is 2% and expectations are formed adaptively, what is the natural rate of unemployment in the economy? (a) 3% (b) 1% (c) 6% (d) 5%