Both Il nous voit and ils nous voient should be marked as correct, as there is no audible difference
how do you AURALLY tell the difference between this, and if it were "HE sees us"?
Orally, there is no difference between "il nous voit" and "ils nous voient".
I guess French people get used to listening into the context of this kind of thing.
Does "They are looking at us" not also make sense? When I peeked it said voient could also be "look at".
It makes sense, but not the sense expected by verb "voir" = see (not look at/watch) You can see without looking and vice versa.
In dictation, there is no difference in sound between "ils voient" and "il voit". They are homophones and the system accepts the singular for that reason.