Especially if you are not from US (but even if you are), after you throw out there some hypothesis like suggested in the other answer I would ask the interviewer if there is any segment that he believes you should consider and that you missed due to being unfamiliar with the market.
If he gives you an hard time and says “why, what do you think?” I would reply “A good way to check this in a real life case would be to go to jewelry stores and websites and see if they offer gold rings for other occasions than wedding and engagement bands and if so, for which, and then maybe have a chat with the store assistant and ask how their sales are roughly split”. At that point usually the interviewer helps you out by either telling you to ignore other segments or to add specific ones.
If he doesn’t give you an hard time he might ask you to add the “class rings / sports rings” market segment for example.
Hope this helps,