The velocity potential function ϕ satisfy the Laplace equation:\(\frac{{{\delta ^2}\phi }}{{\delta {x^2}}} + \frac{{{\delta ^2}\phi }}{{\delta {y^2}}} + \frac{{{\delta ^2}\phi }}{{\delta {z^2}}} = 0\) Then the flow is:

• A. Unsteady, incompressible, rotational
• B. Steady, compressible, rotational
• C. Steady, incompressible, irrotational
• D. Unsteady, compressible, irrotational