Exam question: changing from active to passive voice

Question

the below-mentioned question is asked in my exam, I think my answer is correct, please tell if I am right, I have to challenge the question in 2 days if its answer given is wrong.

correct answer is given by examiner.
candidate answer is the answer I ticked as correct.

In the following question, a sentence has been given in Active/Passive voice. Out of the four alternatives suggested, select the one which best expresses the same sentence in Passive/Active voice.

I will keep your secret.

Options:

1) Keeping of your secret will be done by me.
2) I will be keeping the secret of you.
3) Your secret would be kept by me.
4) Your secret I will be keeping.

Correct Answer: Your secret would be kept by me.
Candidate Answer: Keeping of your secret will be done by me.

Answer 1

The given sentence is in the active, and the test requires that the answer use the passive voice. (2) and (4) are active voice.

Answer (1) is a possible, it creates a gerund phrase as the subject. It is possible but it isn't a likely form.

Answer (3) uses the passive voice, but changes the meaning. The word "would" has several meanings, one possibility is as the conclusion to a conditional phrase, in which the condition is not explicit. "Your secret would be kept, (if it wasn't such great gossip)"

So neither is really an acceptable answer. Instead, the most obvious passive form is just "Your secret will be kept (by me)."

Answer 2

I believe this is a question of which one is the best.

Both answers are correct grammar. In fact, I believe that all of the choices except C are correct grammar. But, the Candidate Answer a.k.a yours, is considered "wordy," which means that it requires more words and complex sentence structure than what is needed.

I have to say that the Correct Answer is better than the Candidate Answer.

Does this answer your question?