Answer:
the art or process of producing images by the action of radiant energy and especially light on a sensitive surface (such as film or an optical sensor)
Since 'sullen' and 'moody' mean almost the same, we should find a word that has a similar meaning to 'monotonous'. The word that has the closes meaning to it is 'repetitious', meaning 'tedious, boring, dull'.
I think it's a preposition.
