A second appeal to the High Court under Section 100 of the CPC has a very limited scope. It can only be entertained if it involves a "substantial question of law."
(A) This is the primary requirement; the High Court must formulate the substantial question of law.
(B) The proviso to Section 100(5) gives the High Court the power to hear the appeal on any other substantial question of law not formulated by it, if it deems necessary.
(C) The nature of the first appellate decree (whether contested or ex parte) does not bar a second appeal, as long as the decree involves a substantial question of law.
Since all the above situations are covered under Section 100 and its procedure, "All of the above" is the correct answer.