The correct answer is: A. less than 2000.
Laminar flow is a type of fluid flow in which the fluid particles move in layers, with each layer moving parallel to the next. This type of flow is typically found in low-speed, low-turbulence flows.
The Reynolds number is a dimensionless number that is used to characterize the flow of a fluid. It is defined as the ratio of the inertial forces to the viscous forces in the fluid.
The Reynolds number is typically used to determine whether a flow is laminar or turbulent. A laminar flow will occur when the Reynolds number is less than 2000. A turbulent flow will occur when the Reynolds number is greater than 4000.
The Reynolds number can be calculated using the following equation:
$Re = \frac{\rho v d}{\mu}$
where:
- $\rho$ is the density of the fluid
- $v$ is the velocity of the fluid
- $d$ is the diameter of the pipe
- $\mu$ is the viscosity of the fluid
The Reynolds number is a useful tool for engineers and scientists who study fluid flow. It can be used to predict the type of flow that will occur in a given system, and to design systems that will minimize turbulence.
The other options are incorrect because they do not correspond to the range of Reynolds numbers for laminar flow.