Possibly it's just that no-one thought to add that as a valid translation.
It's equally possible that it's not a good translation. In English when we describe potatoes as 'good' it can mean one of two things: Either they are good potatoes meaning they are undamaged, of a good size or condition; Or we mean they taste or look good (or nice).
The dictionary definition of Nice is "Giving pleasure or satisfaction; pleasant or attractive". In other words nice does not always mean good. The potatoes can be in a good condition without giving pleasure or being attractive.
Some languages would instead use two different words, or as I think might be the case in Portuguese you need to specifically say they 'taste good' or 'look good' if that's what you meant.
Yes, there are three different etymologies of "são":
- (sane) sānus -> sano -> são
- (saint) sānctus -> santo -> são
- (they are) sunt -> son -> são
You can find more information in some dictionaries like Wiktionary
I think somebody had a different answer to alexsolheim, but it was deleted later. Probably the original question was about the difference between these two words:
- são = "sound" as in "sane" (etymology 1 above)
- som = "sound" as in "noise"
"Sound" is just a homonym in English - there are two different etymologies of "sound" similarly to the case of "são". Actually there are more than two: Wiktionary
But it's just a reduction, because in that specific situation, the rest is implied. We use reductions all the time, it would be a mess if Duolingo accepted all possible meanings, for all possible situations. Example?
Um suco de laranja, por favor = A jar/can/glass of orange juice, please