Illi et Greta Thunberg in urbes sunt
what the hell?
Greta Thunberg?¿ bufff...
Why not "salvant"? Because it is late Latin? A wider question: Where should the boundary between acceptable and not acceptable be? The death of Cicero? The death of Augustus? The end of antiquity?
There isn't a hard and fast boundary date between the two.
It accepted 'servat' saying I had a typo in my answer...
The course contributors have no control over what counts as a typo vs an error.