What does a high voltage line indicate when it's fully energized?

When a high voltage line is fully energized, it signifies that there is an active flow of electricity within the line. This active flow indicates that electricity is being transmitted to the connected circuits and appliances. Moreover, the presence of high voltage indicates that there is potential energy available in the line. This potential energy can be converted to kinetic energy to do work, such as powering appliances or machinery.

Thus, the combination of both the active flow of electricity and the potential energy existing in the energized line is accurately captured in the correct option. This understanding is critical when working near high voltage lines, as both the flow and potential for energy can pose safety hazards.