Answer:
D. contact metamorphism
Explanation:
When there's a volcanic activity in certain area, very often it happens that there's magma that intrudes into the cold rock in the surrounding area. The intrusion of the hot magma into the cold rock layers causes big changes into the structure of the rocks. The high temperature and high pressure manage to influence the structure of the preexisting rocks, mostly on the places where the magma touches the cold rocks, leading to the formation of metamorphic rocks. This type of metamorphism is known as contact metamorphism.
This excerpt outlines the important precedent set by the court case Plessy vs. Ferguson. Plessy vs. Ferguson establishes the idea that "separate but equal" facilities are constitutional (aka legal). Essentially, this Supreme Court ruling allows for private and public places to be segregated. The ruling of Plessy vs. Ferguson resulted in segregated facilities all over the country including schools, restauraunts, bus stops, bathrooms, water fountains, etc.
This case is not overturned until 1954, in which the case Brown vs. Board reverses this idea and declares that separate but equal facilities violates the 14th amednment rights of African-American citizens.
I would go on on the first option, population, community, ecosystem. If there is a control on the rapid growth of population, surely, pollution in the whole community will be reduced thus, making the ecosystem well balanced.