What is the irrotationally condition for a conical flow?

• A. Vθ = \(\frac {∂(V_r )}{∂θ}\)
• B. Vϕ = \(\frac {∂(V_r )}{∂ϕ}\)
• C. Vθ = \(\frac {1}{r} \frac {∂(V_θ )}{∂θ}\)
• D. Vθ = \(\frac {∂(V_r )}{∂θ}\)Vr