When Ken comes home from work one day, his neighbor Nick is waiting for him. "Your lawn is a mess," says Nick, "and you really should do something about it." Ken says, "I'm going on vacation tomorrow. Can you get someone to do a nice job on the lawn for me?" Nick says, "Sure." Nick hires Carlos, a professional landscaper, to fix up Ken's lawn and yard. When Ken returns, Carlos presents him with a bill, which was a reasonable amount. Ken says that he never authorized Nick to promise that Ken would pay this amount. Is Ken obligated to pay Carlos? O Yes, because of Nick's express authority. Yes, because of Nick's incidental authority. Yes, because of Nick's ratification authority. O Yes, because of Nick's estoppel authority