As for this problem together with the presented options with it, the most probable answer and the most likely one would be D. on the second ring.
Though the answer would be it depends since there wasn't any information provided about the nature of the answering of the call, whether it is for business or just personal, if it is for business then what kind of business and so on and so forth. Some let the voice mail answer, it is okay to answer the fourth ring, maybe on the first or on the second. So generally speaking, the correct answer would be on the second ring. Letting the voice mail answer is either you aren't available on the moment or of other matters that might be strategic to the receiver of the call. After the fourth ring is just disrespectful, or you are busy at the moment and made time. On the first ring is great and all, but might give the idea that you are doing nothing. On the second ring gives you a moment to prepare to answer, and it isn't that long for the caller to wait to be entertained.
