Which statement is true regarding the operation of most external-gear pumps?

The statement that external-gear pumps can be reversed without modification is accurate. These types of pumps are designed with two interlocking gears that create suction and discharge through their rotation. When the direction of the pump's operation is reversed, the gears will continue to mesh and function appropriately in the opposite direction, allowing for the fluid to be pumped in the opposite way. This capability adds to the versatility of external-gear pumps, making them suitable for applications that may require changing the flow direction without the need for any mechanical alterations.

In contrast, some other pump types may require specific modifications for reverse flow, and pumps designed only for a single direction cannot alter their flow path without such changes. Additionally, external-gear pumps are capable of handling a variety of fluid viscosities, which allows them to function effectively even with thicker fluids, dispelling the notion that they cannot pump viscous fluids.