Why "Το άσπρο βουνό είναι πίσω από το όμορφο ποτάμι αυτό" is wrong?
A similar answer.
"White" can mean: "λευκό" as well?
Yes. And όρος is another (but more official) word for "mountain," while ωραίο is another (even stronger) word for "beautiful."
Τα Λευκά Όρη στην Κρήτη.
Ποταμός is the masculine version of ποτάμι.
Can we say ... το όμορφο αυτό ποτάμι.? Ι thought we could but I got marked wrong.
Sounds a bit poetic, but it's common enough, so it has been added.
Why is not accepted λευκό
It was added some days ago.