Which of the following factors led to theories that Paleo-Indians may have been in Oklahoma as early as 30,000 BCE?

A. Stone tools found at the Cooperton site were more advanced than expected.
B. Bison bones found at the Burnham site dated back to before 10,000 BCE.
C. Mammoth bones found at the Cooperton site were dated earlier than expected.
D. Clovis Indians arrived in Oklahoma before 10,000 BCE.