Stabler's last appearance was in season 12. He left the show in an announcement in the first episode of Season 13. The original cast members answer does not work.
The quiz is a little too specific, no options for Olivia's mother death (would it accept fell down the subway stairs? Didn't accept fell down the stairs), the "original" cast was never in one season all together as the main cast, I'm not even sure there was a season where all of them appeared. Jeffries has a typo, Stabler's last episode was in season 12.