During the formation of metamorphic rocks, what most likely causes pressure to increase?

Magma pockets rise.

Gravity pulls on rocks.

Rocks melt deep beneath Earth’s surface.

Rocks beneath Earth’s surface are forced toward the mantle.

Consider the following reactions. (note: (s) = solid, (l) = liquid, and (g) = gas.) mg(s) + ½o2(g) → mgo(s) + 146 kcal/mole h2(g) + ½o2(g) → h2o(g), δh = -57.82 kcal/mole what type of reaction is represented by the previous two examples?