Which condition describes laminar flow?

Laminar flow is characterized by the smooth, orderly movement of fluid layers sliding past one another in parallel paths. This type of flow typically occurs at lower velocities and with fluids of higher viscosity, where the inertial forces are not strong enough to disrupt the flow patterns. In laminar conditions, the fluid particles follow a predictable flow line, which minimizes chaotic mixing and turbulence between the layers.

The other conditions do not accurately describe laminar flow. Sudden turbulence pertains more to turbulent flow, where chaotic and irregular fluid movement occurs. High velocity can also indicate turbulent conditions where the flow becomes unstable. Maintaining constant pressure may apply to various flow scenarios but does not specifically relate to the orderly, even behavior indicative of laminar flow. Thus, option A is the clear and accurate description of laminar flow dynamics.