Which is a cause of system unavailability?

A Natural disaster

B incomplete testing

C poor password practice

D poor physical security

D poor physical security

Explanation:

System Unavailability can be caused by the problems that the servers can have, this can be caused by natural disasters, or by troubles with the connection, this is caused by poor physical security because that can cause cables and intallations to be damaged and that can cause a system to become unavailable.