On the Display Network, enhanced cost–per–click (ECPC) automatically:

sets bids to help you get as many conversions as possible
adjusts your manual bid up or down based on each click’s likelihood to result in a conversion
sets bids to maximize your conversion value while trying to reach an average return on ad spend
sets bids to help you get the most clicks within your target spend amount

The correct answer is:

adjusts your manual bid up or down based on each click’s likelihood to result in a conversion.