We reject the options a) and b) since the question says that the data supports "equally" both cases - so we have no basis for making a choice either way.
Further, in science the decisions are reached based on facts, not voting, so we also reject the answer D .
We are left with the answer C and this is also the best practice in science - when unsure, leave it as a hypothesis.
I think the correct answer from the choices listed above is the last option. The control group to be used to test the hypothesis would be the swallows with average-length tails. A control group <span>is defined as the </span>group<span> in an experiment or study that does not receive treatment by the researchers.</span>
The question is asking the determine the role that the United States do in the ecosystem base on the passage and situation in the question that you have state, base on my research, I would say that its role is a Dominant. I hope you are satisfied with my answer and feel free to ask for more if you have question and further clarification