Which formula does Google use to rank keyword-targeted ads on Google search?

Which formula does Google use to rank keyword-targeted ads on Google search?

A) (Maximum cost-per-click (CPC) bid x Quality Score) / Daily Budget
B) (Maximum cost-per-click (CPC) bid + Daily Budget) / Quality Score
C) Maximum cost-per-click (CPC) bid x Quality Score
D) Maximum cost-per-click (CPC) bid only

Answer: C