Non-Native Species Can Increase in Population and Become Pests to an Ecosystem

Non-native species can increase in population and become pests to an ecosystem. Which of the following reasons best describes why this can happen?

A) Non-native species do not always have natural predators.
B) Non-native species may not have natural parasites that control their populations.
C) There may not be any local competitors for the non-native species.
D) Both a and b
E) All of the above