Which of the following BEST ensures timely and reliable access to services?

= According to the CISM Review Manual, availability is the degree to which information and systems are accessible to authorized users in a timely and reliable manner1. Availability ensures that services are delivered to the users as expected and agreed upon. Nonrepudiation is the ability to prove the occurrence of a claimed event or action and its originating entities1. It ensures that the parties involved in a transaction cannot deny their involvement. Authenticity is the quality or state of being genuine or original, rather than a reproduction or fabrication1. It ensures that the identity of a subject or resource is valid. Recovery time objective (RTO) is the maximum acceptable period of time that can elapse before the unavailability of a business function severely impacts the organization1. It is a metric used to measure the recovery capability of a system or service, not a factor that ensures timely and reliable access to services. References = CISM Review Manual, 16th Edition, Chapter 2, Information Risk Management, pages 66-67.