What is a selective collective control system used for?

A selective collective control system is primarily designed for handling elevator operations efficiently. Its main function is to manage multiple calls for elevators while minimizing waiting times and travel times, particularly when elevators may have to travel in opposite directions to service requests.

In this context, option B is correct because selective collective control allows for the prioritization of calls based on the current direction of the elevator and the destination of the passengers. For instance, if an elevator is already going up, and there are calls for an elevator to go down, this system can effectively bypass those calls, ensuring that the elevator operates in the most efficient manner during its journey.

The other options do not relate closely to the specific purpose of a selective collective control system. Managing electrical currents, limiting the speed of hydraulic lifts, and monitoring machine temperatures are tasks that pertain to different types of control systems or equipment, not the operations of elevators specifically.