Which of the following is a right that is guaranteed to U.S. citizens?

Freedom of speech is a fundamental right guaranteed to U.S. citizens by the First Amendment of the Constitution. This amendment protects individuals from government restrictions on expressing their thoughts, beliefs, and opinions. It is a foundational element of democratic society as it allows for open discourse, discussion, and debate, which are essential for a healthy democracy.

In contrast, the other options do not represent guaranteed rights under the Constitution. The right to free healthcare, for example, is not provided as a constitutional right, and access to healthcare can vary based on different factors including insurance and state policies. Similarly, the right to travel is generally unrestricted, allowing citizens to travel freely both within and outside the U.S., rather than being limited to travel within the country alone. There is also no constitutional guarantee of free education for life, as education policies can be influenced by local, state, and federal regulations, and typically involve some form of cost. Thus, freedom of speech stands out as a clearly defined constitutional right.