$19.$ In a forecasting model, at the end of period $13,$ the forecasted value for period $14$ is $75.$ Actual value in the periods $14$ to $16$ are constant at $100.$ If the assumed simple exponential smoothing parameter is$0\mathrm{.}5,$ then the MSE at the end of period $16$ is: A$.820\mathrm{.}31$ B$.273\mathrm{.}44.43\mathrm{.}75$ D$.14\mathrm{.}58$