Final answer:
The United States has a trust responsibility to act in the best interest of American Indian tribes, making the correct answer D. Sovereign.
Step-by-step explanation:
The correct answer is D. Sovereign.
Native American tribes in the United States are considered sovereign nations. This means that they have their own self-governing authority and are recognized as separate political entities. The U.S. government has a trust responsibility towards these tribes, which means that it is obligated to act in their best interest and protect their rights.
For example, the federal government holds title to tribal land in trust on behalf of the tribe, meaning that it manages the land for the benefit of the tribe. This trust responsibility is an important aspect of the United States' relationship with Native American tribes.