What information does the Conversion Optimizer need in order to find the optimal cost-per-click (CPC) bid for an ad each time the ad is eligible to appear?

What information does the Conversion Optimizer need in order to find the optimal cost-per-click (CPC) bid for an ad each time the ad is eligible to appear?

§  Manual bid changes
§  Historical conversion data
§  Test conversions

§  Forecast data