The correct answer is: A. Hot reserve
A hot reserve is a type of generating capacity that is available for service under emergency conditions. It is not kept in operation but is kept in working order so that it can be quickly brought online if needed. Hot reserve is typically used to provide backup power during outages or other disruptions to the power grid.
A cold reserve is a type of generating capacity that is not kept in operation and is not in working order. It would take some time to bring a cold reserve online if needed. Cold reserve is typically used to provide backup power during long-term outages or other disruptions to the power grid.
A spinning reserve is a type of generating capacity that is kept in operation but is not currently providing power to the grid. It is used to provide a buffer against unexpected changes in demand or supply. Spinning reserve is typically used to maintain the stability of the power grid.
Firm power is a type of generating capacity that is guaranteed to be available to meet demand. It is typically used to provide baseload power, which is the minimum amount of power that is always needed to meet demand. Firm power is typically generated by large, reliable power plants such as nuclear power plants or hydroelectric power plants.