Which of the following is true

A. The Original Phillips Curve relation has proven to be very stable across countries and over time

B. Expected inflation always equals actual inflation

C. In the late 1960s, the economists Milton Friedman and Edmund Phelps said policymakers could achieve low rate of unemployment as they wanted as long as they are willing to tolerate inflation

D. Policymakers can exploit the inflation - unemployment trade off only temporarily.

E. The natural rate of unemployment is constant overtime within a country