This is one of the observations that lead linguist Noam Chomsky to conclude that humans have a language acquisition device in our brains: small children extract the rules of grammar and don't just imitate what they here adults say. Саша our small toddler is having to do it twice - English with Dad, and Russian with Mom.
Persons is a perfectly fine word... But probably not in the contexts a toddler would use it in (see, for example, https://www.merriam-webster.com/words-at-play/people-vs-persons).
So this is a masculine noun. http://dictionary.reverso.net/russian-english/%22%D1%83%D1%87%D0%B8%D1%82%D0%B5%D0%BB%D1%8C
but I thought this discussion was about "твоя вещь" translated as "your thing" http://dictionary.reverso.net/russian-english/%D0%B2%D0%B5%D1%89%D1%8C
I suggest having the translation appear on the exercises after they have been completed.
I saw this thread and got confused about what TheHerring meant too - but for me your discussion also came up on a question where you were given several feminine nouns after ТВОЯ but only ВЕЩЬ was accepted.
All that to say, I also want to know why this was the only possible answer... :)
вещь (veščʹ) [vʲeɕː] f inan (genitive ве́щи, nominative plural ве́щи, genitive plural веще́й) "thing, object; things, belongings" From Old East Slavic вещь (veščĭ), borrowed from Old Church Slavonic вещь (veštĭ), from Proto-Slavic *veťь, from *vektь, from Proto-Indo-European *wekti-(“cause, sake, thing”), from *wekʷ- (“to speak”). Morphologically *vek- + *-tь. Cognate with Proto-Germanic *wihtiz, whence English wight ("supernatural creature") and whit ("extremely unimportant thing"), Gothic