Which of the following is a characteristic of a positive displacement pump?

A positive displacement pump is designed to move a fixed volume of fluid with each cycle of the pump, which leads to its defining characteristic of providing constant flow rates. This constant flow occurs regardless of the pressure in the system, as the pump displaces the same amount of fluid with each stroke or rotation. This reliability and predictability make positive displacement pumps particularly useful in applications where consistent flow is critical.

When considering other characteristics, while some pumps may require regular maintenance, this is not unique to positive displacement pumps; all types of pumps have maintenance needs. Additionally, energy efficiency can vary based on the specific design and application, and while some positive displacement pumps may not be as efficient as other types under certain conditions, this is not a defining characteristic of the type itself. Thus, the distinct feature of providing constant flow rates under varying pressure is what confirms the correctness of this choice.