Conversation so far:
What AKB48 events with Promotion and Media happened?
AKB48 has publicized special events to choose the promotional and recording lineups for some of its singles.
What was one of AKB48's publicized special events to choose the promotional and recording lineups for some of its singles?
In 2009, the concept of senbatsu sōsenkyo was introduced, which allowed fans to vote their favorite AKB48 members into the promotional line up for one of their annual singles.
Who did fans vote for their favorite AKB48 members into one of their annual singles?
What other AKB48 events with Promotion and Media were there besides in 2009 with the concept of senbatsu sōsenkyo?
Another selection method, AKB48's rock-paper-scissors tournaments, was introduced in 2010 for the group's 19th single and has recurred as an annual event.
What did AKB48's rock-paper-scissors tournaments involve?
Members of AKB48 and its sister groups compete in the knockout tournament to be part of the recording and promotional lineup for the group's next single.
What happened with AKB48's rock-paper-scissors tournament in 2010?
Starting with 2014, the AKB48's rock-paper-scissors tournament does not determine the promotional line up of a single anymore.

Question: what was the single?
Self-contained rewrite: What was the AKB48 single involved with the rock-paper-scissors tournament?