Which of the following sets of equations represent possible incompressible flow cases?

(a) \(V_{r}=U \cos \theta ; V_{\theta}=-U \sin \theta\)

(b) \(V_{r}=-q / 2 \pi r ; V_{\theta}=K / 2 \pi r\)

(c) \(V_{r}=U \cos \theta\left[1-(a / r)^{2}\right] ; V_{\theta}=-U \sin \theta\left[1+(a / r)^{2}\right]\)