What kind of system allows for call reversal in elevators?

The option indicating "high and low call reversal" is correct because this system specifically allows for the reversal of an elevator call when two or more calls are made in different directions, such as a call to go up from the ground floor while another call requests down from a higher floor. This system intelligently manages the elevator's travel path to optimize efficiency and service by automatically reversing its direction when necessary based on the highest and lowest requested floors.

In contrast, a single call system operates by responding to one call without reversing or adjusting to other calls, making it less versatile. An independent control system refers to separate controls for multiple elevators but does not inherently include call reversal as a feature. A sequential call system may use a predetermined order to service calls but does not specifically indicate the ability to reverse direction based on different call requests. Understanding the nuances of these systems is crucial as they impact how effectively and efficiently elevators serve multiple passengers in a building.