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?

A) Manual bid changes
B) Forecast data
C) Historical conversion data
D) Test conversions

Answer: C