It is exceedingly difficult to tell when you want "a," when you want "the," and when you want the plural, even though it looks like all of them would be appropriate translations for this sentence.
Surely, I know that they always only want "a" to be used when "mot" is used. Here, however, would this sentence only be asking about one stone, the stone the speaker and hearer both have in mind? Or is it asking about stones in general, the nature of stones? If it is the latter, then it would more properly be translated as "Can a stone walk?" or "Can stones walk?" even though the sentence might not use "mot" in Vietnamese. My question is really, I suppose, how one would ask that general question, and whether this is an instance of such a question. I do apologize for my confusion.
This is actually an internal rule of Duolingo. In spoken Vietnamese you will not find this rule applied so often and it is up to you to interpret the context alone.
In this case the sentence is so simple that it's easy to think, "I know what this means!", forget this little rule instilled into us by Duolingo and just tap out the MUCH MORE natural translation of "Can a stone walk", i.e., the whole category of stones, which is exactly what the Vietnamese means in this sentence.
Not to mention that "a"="một" rule is a much better tool in helping us know when to use "một" in translations INTO Vietnamese, and shouldn't be used to nitpick perfectly good English answers ̣(which completely distrupts the flow of learning).
Funny that my translations into Vietnamese are almost always correct while my English ones are wrong about 50% of the time. I wonder where the problem lies - in my English or in Duolingo (for the record, I'm English, btw)
Actually stones, or the stoned, walk in Racetrack Playa in Death Valley National Park , USA...not to be confused with Washington DC...
Is this a common saying that has meaning in Vietnam? I've never had a reason to ask someone if stones can walk.