Answer: a. gneiss
Step-by-step explanation:
Metamorphism can be defined as the synthesis or formation of minerals or rocks from the pre-existing rocks. This involves various physical and chemical processes. The physical processes include the application of heat and pressure. The chemical processes include the oxidation, reduction and other chemical reactions occurring within the rock. Gneiss is one of the highest grade of metamorphic rock. As it exhibit the coarsest grain size. Quartz, mica, and feldspar are the examples of gneiss.