The Term $b _ { 1 }$ In the Equation $\ddot { y } _ { t } = b _ { 0 } + b _ { 1 } t + b _ { 2 } Q _ { 1 } + b _ { 3 } a _ { 2 } + b _ { 4 } Q _ { 3 }$

Multiple Choice

The term $b _ { 1 }$ in the equation $\ddot { y } _ { t } = b _ { 0 } + b _ { 1 } t + b _ { 2 } Q _ { 1 } + b _ { 3 } a _ { 2 } + b _ { 4 } Q _ { 3 }$ , where ?_t represents the predicted value of y at time t, is:

A) the time trend.
B) the seasonal trend.
C) an indicator variable.
D) a value between 0 and 4.