SANTA CLARA, Calif. -- The San Francisco 49ers' offense has taken it to the next level in the six games since star receiver Michael Crabtree has returned from a torn Achilles injury in May.Before Crabtree's return, the 49ers' offense lacked dimension and spark. Now, it is a varied, dangerous offense. His return is a major reason why the 49ers are preparing to play in the NFC championship at Seattle on Sunday.Crabtree's coaches are not taking his return for granted.