9. The system of claim 8 , wherein the operations further comprise identifying, based on the user search activity, a set of follow-up queries for the query pair, each follow-up query in the set being a query that was received following receipt of the first query and the second query in at least one previous user search session, the set of follow-up queries including the third query.
10. The system of claim 9 , wherein the operations further comprise selecting, for providing to the user device, the third query from the set of follow-up based on the ratio meeting the query suggestion threshold frequency.