In which situation would a forest most likely be sustainable? a. when supply exceeds

The answer would be A. When supply exceeds demand

This is because there is plenty supply for the forest without animals dying from things such as, lack of food.

When demand exceeds supply it throws an ecosystem off because some animals aren't getting the food they need and therefor dying. So that eliminates answers C. and D. 

When supply and demand are both 0 that means that there are no animals to demand and there are no supplies for demand leaving no sustainable ecosystem.

A. When supply exceeds demand (APEX)

Another answer for apex users is "When supply is greater than demand."

B. The Clean Water Act.

Explanation:

This law came into place in the United States of America in the year 1972 during the 20th century and has maintained the law and control of clean distribution, usage and consumption by people the said country.

The Clean Water Act are laws found and are enforced in the United States Of America. It is a federal law whose works governs water pollution, and is administered by state environmental agencies and also EPA.