Answer:
C. He has been a champion of social change in athletics.
Step-by-step explanation:
Gregg Popovich is a credible source for the author to cite because he has a long history of actively advocating for social change in athletics. He has spoken out in favor of Black Lives Matter and spoken out against police brutality. He has also been a vocal critic of President Trump and his policies. Popovich has become known as a leader in the fight for social justice in athletics.