_______ conductors are permitted to be attached to and supported by the service mast.

Service drop conductors are specifically designed to connect the utility's overhead lines to a building's service entrance. They are typically supported by the service mast, which is the vertical section of conduit or support structure that connects the service drop to the building. The service mast provides the necessary structure to securely hold the service drop conductors in place, ensuring safety and compliance with the National Electrical Code (NEC) regulations.

This answer reflects a clear understanding of the roles and specifications related to service drops and their installation. Given their purpose and construction, service drop conductors are the only type that is explicitly permitted to be attached and supported by the service mast. This requirement is crucial for maintaining proper electrical safety and system integrity.