Answer:
A. the food web
Explanation:
Ecosystems have lots of different living organisms that interact with each other. The living organisms in an ecosystem can be divided into three categories: producers, consumers and decomposes. They are all important parts of an ecosystem. Producers are the green plants.
It regulates on/off like a light switch
Calcium deficiency disease (hypocalcemia) --- like osteoporosis, osteopenia !!
