The continuity equation in a differential form is
$(a) \frac{dA}{A}+\frac{dV}{V}+\frac{d\rho }{\rho }=constant$
$(b) \frac{A}{dA}+\frac{V}{dV}+\frac{\rho }{d\rho }=constant$
$(c) \frac{dA}{A}+\frac{dV}{V}+\frac{d\rho }{\rho }=0$
$(d) A dA+V dV+\rho d\rho =0$