'Satisfying' You can't say 'satisfaction' because that's a noun. 'Satisfies' is a verb, so you can only say that if you remove 'is'. 'Satisfied' and 'satisfying' are the only ones that work grammatically, because they're both adjectives. 'Satisfied' however makes no sense logically, because the act of finishing a test isn't something that can experience satisfaction (ie. 'to be satisfied' describes the object of 'satisfy' and 'to be satisfying' describes the subject - these adjectives are derived from the passive voice and present continuous forms of 'satisfy' respectively).

D - It is satysfying