The integrating factor of the differential equation $\large\frac{dy}{dx}$$+py=Q$ is

Question

\[\begin{array}{1 1}(1)\int\mathrm{pdx}\,&(2)\int\mathrm{Q}\,\mathrm{dx}\\(3)\int\limits_{e}\mathrm{Q}\,\mathrm{dx}&(4)\int\limits_{e}\mathrm{p}\mathrm{dx}\end{array}\]