The correct answer is: B. base load plants
Base load plants are power plants that are designed to operate at a constant output, regardless of the demand for electricity. They are typically used to provide a steady base of electricity to the grid, while other plants are used to meet peak demand.
Base load plants are typically the most efficient type of power plant, as they can operate at their full capacity for long periods of time. They are also typically the most expensive type of power plant to build, as they require large amounts of fuel and equipment.
Peak load plants are power plants that are designed to operate at a high output during periods of peak demand. They are typically used to meet the increased demand for electricity during times of high usage, such as hot summer days or cold winter nights.
Peak load plants are typically less efficient than base load plants, as they are not designed to operate at their full capacity for long periods of time. They are also typically less expensive to build than base load plants, as they require less fuel and equipment.
Neither (A) nor (C) is correct, as base load plants are not normally used as peak load plants, and peak load plants are not normally used as base load plants.