C: internal unstable; internal stable

    Incorrect.
An internal unstable attribution of academic failure is attributing your poor performance to factors such as: lack of effort, or lack of interest in the subject.  An example of an internal stable attribution regarding the cause of academic failure would be lack of ability or lack of discipline.  If this was the goal of attributional retraining, it would cause students to perform more poorly.  Changing the attribution that you do poorly because you don't study enough (internal unstable) to the attribution that you have no ability (internal stable) would cause a person to feel helpless in improving, because they lack ability, and can not get any better.