Q. What do you mean by Conditional selection?
Conditional selection: When a marker is instructed to create a connection from a given incoming trunk to a given outgoing trunk, this also describes the link to be used and select and bridge magnets to be operated to make the connection. Maker doesn't make the connection till it interrogated busy/free condition of the outgoing trunk and of relevant link. Only if both are found to be free does it operate switches. This is known as Conditional Selection.