Question: With Google's Active View technology, when is an impression of a display ad considered viewable?

1. when the user leaves the page the ad appears on
2. when any part of the ad is on-screen for 5 seconds
3. when the entire ad first appears on the screen
4. when at least 50% of the ad is on-screen for at least 1 second

Answer: The correct answer of the above question is Option D:when at least 50% of the ad is on-screen for at least 1 second