Answer:
Explanation:
Organisms have different forms of circulatory systems. Humans have a closed circulatory system, while many mollusks and other invertebrates have an open system. In a closed circulatory system, blood is enclosed within blood vessels.
Answer:Succession as progressive change in an ecological community. Primary vs. secondary succession. The idea of a climax community.
Explanation:
The answer is B An observation about the number or amount of something