Which of these will satisfy the continuity equation?

Question

Consider the following:

The components of velocity u and v along X and Y directions in a 2D flow problem of an incompressible fluid are

1.  U = x² cos u; v=-2x sin y

2.  U = x+2; v=1-y

3.  U= xyt, v=x³ – y² t/2

4. U = In x+Y; v = xy –y/x

Which of these will satisfy the continuity equation?

(A) 1, 2 and 3 only (B) 1, 2 and 4 only

(C) 2, 3 and 4 only (D) 1, 2, 3 and 4