Final answer:
Once a user hits the frequency cap for an ad, that particular ad ceases to serve to them to avoid overexposure. The ads from that campaign are temporarily halted, but the placement will continue to show other ads to different users.
Step-by-step explanation:
When a user meets the frequency cap for an ad, it typically means that the ad will no longer be served to that user until a specified time has elapsed. The correct answer to the student's question is: 1) Ads stop serving to that user. This is because a frequency cap is a restriction designed to limit the number of times a single user sees the same ad within a specific time frame to prevent overexposure and potential annoyance. Once this cap is hit, other ads may rotate in or the user might simply not see any additional ads from that campaign for a while.
Frequency capping is an important tool for advertisers who want to maintain a good relationship with their audience by not bombarding them with repetitive content. It's worth noting that while the ads stop serving to that user temporarily, the placement itself does not stop serving ads altogether and will continue to serve other targeted ads or default ads to different users.