(a). (4 pts) Define the terms ergodic, stationary, non-stationary (b).(4 pts) How would you test for stationarity? (c).(4 pts) Explain the problem of spurious regression and relate it to the question of stationarity of the time series data( (d). (4 pts) When does non-stationary time series data not give rise to the problems of a spurious regression