D

The only one which sounds both grammatical and idiomatic to me is D. You could perhaps make a case for A and C being grammatical but no-one talks like that. B is ungrammatical. I'm afraid though I don't know what the Chinese says! I'm just replying because no-one else has after 7 hours. A and B should both be "more of a success than". C should really read like D. I hope that helps to some extent.

The examiner could be looking for B as the correct answer; however we usually add the word 'of' to read 'more of a success than . .' Another way of saying this would be '. . was more successful than . .' D is grammatically correct but is ambiguous as it could mean that the anticipated outcome is what actually happened, or imply that a better outcome would have been preferred, but that there had been doubt about this happening. Only a good knowledge of the background to the statement could differentiate between these two possibilities. I suspect that this is the 'correct answer' that the examiner is looking for.

D A would be corrected as: "a success greater than" B would be corrected as: "more successful than" C would be corrected as: "a success as great as" or "as successful as"