Explain Conditional selection.

Conditional selection: While a marker is instructed to establish a connection from a specified incoming trunk to a specified outgoing trunk, it also defines the connection to be used and choose and bridge magnets to be operated to create the connection. The maker does not make the connection till this interrogated the busy/free condition of the outgoing trunk and of the relevant link. Simply if both are determined to be free it does operate the switches. It is termed as Conditional Selection.