The Database Resource Manager is not currently active in your database that is up and running. You created a resource plan named DAY_PLAN that contains two sub-plans named MANAGERS_PLAN and CLERKS_PLAN. You decided to activate DAY_PLAN by executing the following statement： SQL>ALTER SYSTEM SET RESOURCE_MANAGER_PLAN = ’managers_plan’； What will be the outcome of this statement？（）

A. The statement will deactivate DAY_PLA
B. The statement will activate DAY_PLAN as the top plan.
C. The statement will activate MANAGERS_PLAN as the top plan.
D. The statement will return an error because MANAGERS_PLAN is not the top plan.