SANTA CLARA, Calif. -- Here is a look at what the San Francisco 49ers must do and can't do Sunday at Seattle in the NFC title game:Must happen: The 49ers have to win the turnover battle. I don't think they can afford to lose one turnover and they have to force Seattle into, at least, two turnovers. This is going to be a tough-and-tumble game. San Francisco will need some breaks and can't make silly mistakes.Can't happen: The 49ers can't crumble because of the crowd noise.