What part of an experiment serves as a comparison for the results?

Coquina, a type of limestone, forms from shell fragments that settle on the ocean floor. what type of rock is coquina?

Anybody who knows ap biology, can you friend or message me

Fossils of ancestors of the modern horses show a small 4-toed almost dog-like browsing animal named eohippus over time the horses got larger lost toes and changed to a grazing diet what is the best explanation of why this change occurred