You Are "Living Off the Grid",meaning That You Are Not

Multiple Choice

You are "living off the grid",meaning that you are not using any public utilities---no water supply,no sewer connection,no natural gas or electricity.You do have a septic tank,whose pipe carries sewage out into the back yard.There is also a small pond out there that you have stocked with fish.However,you notice that the fish are floating dead in the water,and the pond seems to have a green scum on it.What has happened?

A) Chemical toxins from your septic tank cleaner have killed the fish.
B) There are not enough nutrients in the water,so the fish died.
C) There is oxygen depletion in the pond due to the leakage of phosphates and other compounds from your septic tank.
D) The fish died due to a lack of calcium,which then caused the algae to overgrow.