Could "This is not the Spanish flag" also work? That's what I put and got it wrong. :-/
Yes, the course is full of these cases where they only accept "x of y" instead of "y's x".
"this is not the Spanish flag" - much more natural
❤❤❤❤❤❤❤❤ Vietnamese program
I must agree: this is an unnatural manner of speaking for a native speaker. It might get fixed when an admin gets around to it; heaven knows they must get a lot of suggestions from users...