Please choose the correct answer to the question: Which of the following organisms have the greatest effect on an ecosystem because of the changes they make to their environment?

Answer1: bees building a hive in a hollow tree Answer2: wasps building a nest in a leafy bush Answer3: beavers building a dam across a stream Answer4: fish digging a burrow on a river bottom

Answer format: answer1/answer2/answer3/answer4
Answer: answer3