Here's a problem to solve: Human interaction with the environment has led to increasing amounts of acid rain. Which population have humans adversely affected the most by contributing to the production of acid rain?

Among the 4 following options, which is the correct answer?

- A: frogs in a pond ecosystem
 
- B: fish in an ocean ecosystem
 
- C: bears in a tundra ecosystem
 
- D: lions in a grassland ecosystem
 