If There Are T Observations (Y_i,x_i)to Estimate the Lagged Regression

Multiple Choice

If there are T observations (y_i,x_i) to estimate the lagged regression model y_t = β₀ + β₁x_{t - 1} + ε_t,what is the actual number of observations used to make the forecast for time period T?

A) T - 1
B) T + 1
C) 1 - T
D) T