<P> One of the challenges in defining death is in distinguishing it from life . As a point in time, death would seem to refer to the moment at which life ends . Determining when death has occurred is difficult, as cessation of life functions is often not simultaneous across organ systems . Such determination therefore requires drawing precise conceptual boundaries between life and death . This is difficult, due to there being little consensus on how to define life . This general problem applies to the particular challenge of defining death in the context of medicine . </P> <P> It is possible to define life in terms of consciousness . When consciousness ceases, a living organism can be said to have died . One of the flaws in this approach is that there are many organisms which are alive but probably not conscious (for example, single - celled organisms). Another problem is in defining consciousness, which has many different definitions given by modern scientists, psychologists and philosophers . Additionally, many religious traditions, including Abrahamic and Dharmic traditions, hold that death does not (or may not) entail the end of consciousness . In certain cultures, death is more of a process than a single event . It implies a slow shift from one spiritual state to another . </P> <P> Other definitions for death focus on the character of cessation of something . In this context "death" describes merely the state where something has ceased, for example, life . Thus, the definition of "life" simultaneously defines death . </P> <P> Historically, attempts to define the exact moment of a human's death have been subjective, or imprecise . Death was once defined as the cessation of heartbeat (cardiac arrest) and of breathing, but the development of CPR and prompt defibrillation have rendered that definition inadequate because breathing and heartbeat can sometimes be restarted . Events which were causally linked to death in the past no longer kill in all circumstances; without a functioning heart or lungs, life can sometimes be sustained with a combination of life support devices, organ transplants and artificial pacemakers . </P>

Which of the following is an indicator of time of death