The number of legs that an arthropod has is a very useful characteristic for classifying them into different classes. Insects always have six legs<span> (three pairs) and arachnids have </span>eight legs<span> (four pairs). Crustaceans have at least </span>eight legs<span> and often more, while myriapods can have up to a hundred legs!</span>
The answer is
B) Evolution
I think its a and b, but i dont know what kind of rock it is. my guess is a metamorphic or sedimentary.