Dynamic remarketing lets an advertiser:

• show prior visitors to his site ads that are based on products or services they saw on the site
• show an ad to someone on his mobile device 24 hours after visiting the website on a desktop PC
• re–run an ad to increase the volume of people who will see it
• engage visitors to the website by opening a chat session

The correct answer is:

• show prior visitors to his site ads that are based on products or services they saw on the site.