If the Temperature in the Earth Generally Increases with Depth

If the temperature in the Earth generally increases with depth, how is it possible that the inner core is a solid?

A) Temperatures increase to a certain point before leveling off below the melting point of the core.
B) The pressures in the core are immense and keep it in a solid state in spite of the temperature.
C) Earth's interior does not reach temperatures high enough to melt the material of the inner core.
D) The inner core is shedding the heat so quickly that melting does not have time to occur.