bees building a hive in a hollow tree wasps building a nest in a leafy bush beavers building a dam across a stream fish digging a burrow on a river bottom
I am hesitating between 4 options to answer the following question, which option should I choose?
Question: Which of the following organisms have the greatest effect on an ecosystem because of the changes they make to their environment?
Possibilities:
- bees building a hive in a hollow tree
- wasps building a nest in a leafy bush
- beavers building a dam across a stream
- fish digging a burrow on a river bottom

beavers building a dam across a stream