The differential equation satisfied by all the straight lines in $xy$ plane is

Question

$$\begin{array}{1 1}(1)\frac{dy}{dx}=a constant&(2)\frac{d^{2}y}{dx^{2}}=0\\(3)y+\frac{dy}{dx}=0&(4)\frac{d^{2}y}{dx^{2}}+y=0\end{array}$$