A

Step 1: Understand that in a cylindrical tube, the velocity profile of a viscous fluid typically follows a parabolic shape due to the no-slip boundary condition at the walls.
Step 2: Option A shows this parabolic velocity distribution with the maximum velocity at the center and decreasing velocities towards the walls, aligning with the expected behavior of laminar flow in a circular tube.
Step 3: Options B and C depict non-laminar flow or irregular velocity distributions, which do not accurately represent the behavior of viscous fluids in a cylindrical tube.
Therefore, the best representation is Option A.