If 'm' and 'n' are the degree and order respectively of the differential equation $1 + \left(\frac{\text{dy}}{\text{dx}}\right)^3 = \frac{\text{d}^2\text{y}}{\text{dx}^2}$, then the value of $(m + n)$ is : (A) 4 (B) 3 (C) 2 (D) 5