What is one obligation that is only for United States citizens?

The obligation that is unique to United States citizens is the requirement to serve on a jury. This civic duty is reserved specifically for citizens because it reflects a significant responsibility in the American legal system, where citizens are called upon to participate in the judicial process and ensure a fair trial. Serving on a jury is fundamental to the rights of a citizen, as it allows them to take part in the administration of justice and uphold the rule of law in their community.

The other options listed, such as obeying local laws, paying federal taxes, and attending school, apply to both citizens and non-citizens residing in the United States. While paying taxes is often seen as a hallmark of responsible citizenship, it is not exclusive to citizens; lawful permanent residents and certain other non-citizens are also required to pay taxes. Similarly, obeying local laws is a general requirement for anyone living in a particular jurisdiction, and education requirements can apply to all children, regardless of their citizenship status. Thus, serving on a jury stands out as a distinctive obligation held uniquely by citizens.