Final answer:
The best rock of a politic protolith from the given options might be quartz arenite, as it is a sandstone composed mostly of quartz grains suitable for undergoing metamorphism into a quartz-rich metamorphic rock.
Step-by-step explanation:
The student's question is about what might represent the best rock of a politic protolith. A protolith is the original, unmetamorphosed rock from which a metamorphic rock forms. Of the options provided, quartz arenite would likely be the best example of a protolith for a quartz-rich metamorphic rock. Quartz arenite is a type of sandstone that is composed almost entirely of quartz grains, making it a suitable candidate for undergoing metamorphism and transforming into a quartz-rich metamorphic rock.