Campaign efficiency is measured by ___. Select all that apply.

ACOS (Advertising Cost of Sales) measures the efficiency of ad spend by showing the ratio of ad spend to sales generated. A lower ACOS indicates higher efficiency. KENP (Kindle Edition Normalized Pages) is a metric for Kindle Direct Publishing authors, measuring pages read in Kindle Unlimited, and while not a universal DSP metric, it's relevant for authors using Amazon Ads to promote their books. CTR (Click-Through Rate) measures the percentage of impressions that result in a click, indicating how engaging an ad is. A higher CTR generally suggests better ad efficiency. Impressions, while important for reach, do not directly measure efficiency as they only indicate how many times an ad was shown, not its performance in driving actions or sales.