Correct Answer: CDTo enforce that a trail record's Effort_Level__c field set to Rigorous requires the distance to be 10 miles or more and the time to complete to be 5 hours or more, the validation rule should trigger an error if either the distance is less than 10 miles or the time is less than 5 hours. The correct validation rule is 'AND(ISPICKVAL(Effort_Level__c, ‘Rigorous’), Distance__c < 10, Time_to_Complete__c < 5)' because this rule becomes true when the distance is less than 10 miles or the time to complete is less than 5 hours, thereby enforcing the required conditions.