An advertiser looking to drive conversions is using manual cost-per-click (CPC) bidding. Which factor should be most important for this advertiser when keyword bids are decided

An advertiser looking to drive conversions is using manual cost-per-click (CPC) bidding. Which factor should be most important for this advertiser when keyword bids are decided?
  A)  The profit derived from a paid click
  B)  The bids of the next closest competitor
  C)  The cost of the bid
  D)  The Quality Score of the keyword