Impressions are based on the ______.

A) viewership ratings of a media outlet
B) potential costs of airtime or media space
C) number of clicks per second on a website
D) profitability of a media investment

Impressions are typically calculated based on the estimated number of people who may have seen an ad or content in a specific media outlet based on their viewership ratings. Other factors like potential costs, number of clicks, and profitability may be considered in media planning and buying, but they are not used to determine impressions.