Answer:
The most common nutrients causing eutrophication are nitrogen and phosphorus. The main source of nitrogen pollutants is run-off from agricultural land, whereas most phosphorus pollution comes from households and industry, including phosphorus-based detergents.
Explanation:
I'm not sure if it's the "best" example but.
If your blood tempature is low, the hypothalamus will issues reflex commands that make your body shiver. If you are hot, you will sweat is the opposite of this.
Another example is, if your blood contains pyrokines then you might have an infection so you begin to run a fever as your body's way to kill the pathogen at the direction of the hypothalamus.
Hope these examples help!
It is A. Those are all decomposers, the other answers like C are all animals. Decomposers are are biotic organisms that break down basically dead plants or animals.