The velocity potential function $$\varnothing$$ satisfy the Laplace equation :
$$\frac{\delta^2 \varnothing}{\delta x^2} + \frac{\delta^2 \varnothing}{\delta y^2} + \frac{\delta^2 \varnothing}{\delta z^2} = 0$$. Then the flow is

A

Unsteady, incompressible, rotational

B

steady, compressible, rotational

C

steady, incompressible , irrotational

D

Unsteady, compressible , irrotational