When Advertising Content Appears to Be Native to a Platform

When advertising content appears to be native to a platform (a news article, independent website, organic search result) , the ethical thing to do is to:

A) warn users beforehand that the platform contains content from advertisers.
B) make sure that users are led to the advertiser's content before native content.
C) charge the advertiser per click and not per view.
D) make the advertisement stand out by using bright colors for the font and background.
E) conspicuously disclose when content is sponsored by an advertiser.