Concept:An appointment can be cancelled or invalidated when found to be based on false or irregular credentials.
Explanation:The sentence says irregularities were discovered in the person's credentials, so the appointment must be made null and void.
The word "annulled" means officially declaring something invalid, which fits this context.
"Terminated" means ended but does not stress the reason of invalidity.
"Suspended" means temporarily stopped, not permanently cancelled.
"Dismissed" usually refers to removing a person from a job, not cancelling the appointment itself.
Therefore, the best word to complete the sentence is "annulled".
Answer:A. annulled