Which of the following acts to keep a rock solid instead of melting) ?

A) an increase in temperature
B) an increase in the vibration within a lattice
C) an increase in confining pressure
D) none of these

An increase in confining pressure acts to keep a rock solid instead of melting by counteracting the tendency of the rock to expand and melt as temperature increases. This pressure effectively keeps the molecules of the rock closer together, maintaining its solid state.