Final answer:
The correct answer is 'concealing' as it is the only option that is nine letters long and fits the context of an actor staying out of the audience's view in a theater setting.
Step-by-step explanation:
An actor is concealing him or herself if he or she stands where the audience cannot see him or her. The answer to the fill-in-the-blank question is concealing, which is the only option among a) Concealing b) Hiding c) Camouflaging d) Conceiving that consists of nine letters and fits the context of the sentence correctly. The term concealing refers to the action of keeping something hidden or secret, which in the context of theatre, would imply that the actor is intentionally staying out of the audience's view.