Submetering, as a Function of Energy-Use Tracking and Recording, Is

Submetering, as a function of energy-use tracking and recording, is:

A) a method of energy management in which meters are installed in energy-using areas to monitor their specific usage.
B) an informative but very expensive tool, even when it is installed during initial construction.
C) a technique used by the utility company in agreement with the user to estimate monthly electricity usage.
D) a method used by utility companies to prevent "brownouts" by substituting purchased and metered electricity from a secondary supplier.