Final answer:
Contact metamorphism occurs when rocks are subjected to the high temperatures from an intruding magma body, not due to higher pressure alone or changes in mineral density or shape. The correct option that would cause contact metamorphism is B. Higher temperature.
Step-by-step explanation:
The process of contact metamorphism occurs when rocks are influenced by the high temperature associated with a nearby or intruding magma body. This heat can cause changes to the surrounding rock, including the recrystallization of minerals and the creation of new mineral assemblages. Contact metamorphism does not typically involve increased pressure or solely the densification or elongation of minerals, but rather the thermal influence on the rock. Therefore, the factor that would cause contact metamorphism is B. Higher temperature.
When evaluating the options, it's crucial to recognize that contact metamorphism specifically refers to metamorphism at the boundaries where rocks come into contact with magma, and it is primarily driven by an increase in temperature.
This distinguishes it from regional metamorphism, which involves changes over broader areas due to increased pressure and temperature typically associated with mountain building.