What counts as a view-through conversion in a TrueView for action campaign?

1. User sees just an impression of the ad and converts within three days.
2. Users clicks on an element of the ad and converts within 24 hours
3. Users clicks on an element of the ad and converts within three three days.
4. User sees just an impression of the ad and converts within 24 hours.

Correct Answer:

4. User sees just an impression of the ad and converts within 24 hours.