How Should Disaster Recovery Drills Be Executed

How should disaster recovery drills be executed?

A) They should be scheduled on a regular basis and everyone involved should be notified of the dates.
B) If the disaster recovery plan is complete and up-to-date drills are not really needed.
C) They should start with a phone call in the middle of the night to all relevant individuals or a surprise announcement during working hours.
D) They should be scheduled on an irregular basis,but everyone involved should have at least a weeks notice to ensure that everyone will be available.