The correct answer is B. The worry that a powerful government would interfere with people's freedom.
Anti-federalists were worried about a powerful central government infringing on the rights of citizens due to their experience as colonists under the control of Great Britain. One of the major causes of the American Revolution is this idea that the central government was acting in a tyrannical way and that this government was violating the rights of the colonists. To preven this from happening again, the Anti-federalists wanted the new constitution to possess a Bill of Rights in order to guarantee certain protections from the government.