Match each differential equation to a function which is a solution.
FUNCTIONS
A. $y = 3x + x^2$,
B. $y = e^{-6 x}$,
C. $y = \sin(x)$,
D. $y = x^{\,\frac{1}{2}}$,
E. $y = 7 \exp(3 x)$,
DIFFERENTIAL EQUATIONS

1. $y' = 3 y$
2. $y'' + y = 0$
3. $xy' -y = x^2$
4. $2x^2y'' + 3xy' = y$