I believe that the answer would be B. Ichthyosaurs. Hope this helps :)
Answer: An environment refers to the surroundings or dwelling place of all living things while an ecosystem is likened to a community that functions as a single unit. When you talk about the environment, it does not include the relationship between organisms and their surroundings, but only the setting or habitat.
Explanation:
Endocrinology. That would be the correct answer. {:)
I don't quite understand the question but if it's a "complete the sentence" then the atomic number is the number of protons or electrons present in an atom.