For steady flow of a viscous incompressible fluid through a circular pipe of constant diameter, the average velocity in the fully developed region is constant. Which one of the following statements about the average velocity in the developing region is TRUE?

• A. It increases until the flow is fully developed
• B. It is constant and is equal to the average velocity in the fully developed region
• C. It decreases until the flow is fully developed
• D. It is constant but is always lower than the average velocity in the fully developed region.