The Energy Emitted by a Star Increases as the Fourth

The energy emitted by a star increases as the fourth power of its surface temperature and a red giant star has a lower temperature than the Sun.Why then is the luminosity of a red giant about a thousand times greater than that of the Sun?

A) A red giant is bigger and therefore has a much larger surface area.
B) The energy transfer from a red giant's interior is much more efficient than the transfer is in the Sun.
C) More of a red giant's total output of energy is in the visible range than is the energy of the Sun, and hence the red giant appears brighter.
D) A red giant's nuclear furnace produces much more energy than does that of the Sun.