Since I don't have access to the diagram you're referring to, I can't match the letters directly. However, I can provide you with a general understanding of the environments of metamorphism in the context of plate tectonics:

a) Contact Metamorphism: This occurs when rocks are subjected to high temperatures and pressures due to contact with magma. It typically occurs in localized areas near igneous intrusions.

b) Regional Metamorphism: This occurs over large areas due to tectonic forces, such as the collision of continental plates or subduction zones. It results in high temperatures and pressures, leading to the transformation of rocks over a wide area.

c) Burial Metamorphism: This occurs when rocks are buried to great depths due to sedimentation or tectonic processes. The weight of overlying materials results in increased pressure and temperature, causing metamorphic changes.

d) Hydrothermal Metamorphism: This occurs when rocks are altered by hot, aqueous fluids circulating within the Earth's crust. It commonly occurs in association with volcanic activity or along fault zones.

e) Impact Metamorphism: This occurs when rocks are subjected to extremely high pressures and temperatures due to the impact of meteorites or asteroids. It leads to localized metamorphic changes around impact craters.