Rockstar Games introduced a game called Grand Theft Auto IV (GTA IV) on PlayStation 3 in April, 2008. Figures 3A and 3B below show the actual monthly unit sales and price over 24 months (Apr. 2008 - Mar. 2010). Figure 3A: Monthly Unit Sales over 24 months Figure 3B: Monthly Unit Sales over 24 months Rockstar Games is interested in understanding the demand for GTA IV, and decided to estimate the following linear demand equation: Q_t=_0+_1 P_t+_2 Holiday_t+_3 ln(t)+_t where t is month (t=1,...,24), Q_t is the unit sales of GTA IV in month t, P_t is the price in month t, Holiday_t is a dummy variable which takes one if month t is December and zero otherwise, ln(t) is the natural log of t, and _t is an error term. Carefully explain the intended role of each independent variable, P_t, Holiday_t, ln(t) and as well as the error term _t in explaining Q_t. [4 points]