Read this: American Idol has traditionally released studio recordings of contestants' performances as well as the winner's coronation single for sale. For the first five seasons, the recordings were released as a compilation album at the end of the season. All five of these albums reached the top ten in Billboard 200 which made then American Idol the most successful soundtrack franchise of any motion picture or television program. Starting late in season five, individual performances were released during the season as digital downloads, initially from the American Idol official website only. In season seven the live performances and studio recordings were made available during the season from iTunes when it joined as a sponsor. In Season ten the weekly studio recordings were also released as compilation digital album straight after performance night.

When did iTunes become a sponsor on American Idol? 
What is the answer? (If it cannot be answered, return "unanswerable")
season seven