$y = ax + b$ is

• A
  General solution of $\frac{d^3 y}{dx^3} = 0$
• B
  General solution for $\frac{dy}{dx} = a + b$
• C
  General solution for both $\frac{d^2 y}{dx^2} = 0$ and $\frac{d^3 y}{dx^3} = 0$
• D
  General solution for $\frac{d^2 y}{dx^2} = 0$