What is the differential equation of gradually varied flow in a wide rectangular channel using Manning's formula?
A) dE/dx = (1/n)(V²/2g)(dV/dx)(dA/dx)(A/P)²/³
B) dE/dx = (1/n)(V²/2g)(dV/dx)(dA/dx)(A/P)³/²
C) dE/dx = (1/n)(V²/2g)(dV/dx)(dA/dx)(A/P)⁵/³
D) dE/dx = (1/n)(V²/2g)(dV/dx)(dA/dx)(A/P)⁷/³