Answer: C!
Step-by-step explanation:
C. "By signing the historic Cobell settlement into law, we established the Land Buy-Back Program..." (paragraph 3)
This statement best reveals the speaker's claim that progress for tribal nations is a collaborative effort because it emphasizes that the progress was only achieved through the collective effort of the President and Congress, who signed the settlement into law. This implies that collaboration between different stakeholders is necessary for lasting progress.