Complex sentence: Lister asks Holly why Rimmer was brought back as a hologram instead of Kochanski because Rimmer was the best person to keep Lister sane, and that the two had shared fourteen million words between each other, compared to the 173 words Lister shared with Kochanski.
Split into simpler sentences: Lister asks Holly why Rimmer was brought back as a hologram instead of Kochanski. Holly explains that this is because Rimmer was the best person to keep Lister sane, and that the two had shared fourteen million words between each other, compared to the 173 words Lister shared with Kochanski.