For the parallelogram OPQR shown in the sketch, $\overrightarrow{OP}=a \hat{i}+b \hat{j}$ and $\overrightarrow{OR}=c \hat{i} +d \hat{j}$. The area of the parallelogram is

1. $ad-bc$
2. $ac+bd$
3. $ad+bc$
4. $ab-cd$