Two dimensional flow occurs when A. the direction and magnitude of the velocity at all points are identical B. the velocity of successive fluid par-ticles, at any point, is the same at suc-cessive periods of time C. the magnitude and direction of the velocity do not change from point to point in the fluid D. the fluid particles move in plane or parallel planes and the streamline pat-terns are identical in each plane

The correct answer is: D. the fluid particles move in plane or parallel planes and the streamline patterns are identical in each plane.

A two-dimensional flow is a flow in which the velocity of the fluid particles is constant in the direction perpendicular to the plane of flow. This means that the fluid particles move in parallel planes, and the streamline patterns are identical in each plane.

Option A is incorrect because the direction and magnitude of the velocity can change from point to point in a two-dimensional flow.

Option B is incorrect because the velocity of successive fluid particles can be different at successive periods of time in a two-dimensional flow.

Option C is incorrect because the magnitude and direction of the velocity can change from point to point in a two-dimensional flow.