A company is developing a linear programming model for its aggregate productionplan. If It $=$ units in inventory at the end of period t$,$ Pt $=$ units produced in period t$,$and D$+=$ demand in period t$,$ then the company's demand constraint to ensure that demand is met in quarter $2$ is

$1)$ D$2=12-11+$ P$2$

$2)$ D$2=11+$ P$2$

$3)$ D$2=12+11+$ P$2$

$4)$ D$2=11+$ P$2-12$