Final answer:
The rock with evenly distributed mineral crystals likely formed under very high temperature and pressure, which corresponds to the conditions required for the formation of metamorphic rocks through recrystallization and other processes.
Step-by-step explanation:
The rock described in the student's question, with light and dark mineral crystals that are evenly distributed, likely formed in an environment with very high temperature and pressure. These conditions are indicative of metamorphic processes, where pre-existing rocks, or protoliths, are altered under subsolidus conditions to create new metamorphic rocks. During metamorphism, changes occur such as the recrystallization of minerals, the formation of new minerals, and in some cases, foliation — the orientation of minerals in a direction perpendicular to pressure. As metamorphism occurs under a range of temperatures and pressures, and the presence of evenly distributed mineral grains typically suggests significant heat and pressure, we can deduce that the correct answer is Option D: Very high temperature and pressure.