"They have the keys."
Translation:Loro hanno le chiavi.
Words that end in -e in the singular all change to -i in the plural. But they can be either feminine or masculine and you just have to learn them. The article (il/la/i/le/etc) is the best way to know. (Duolingo is pretty much always right)
Since it is la chiave (the key) it becomes le chiave (the keys) when plural.
According to the loss of my heart, you're right. I'm learning of course but I thought I had it with "i chiavi". Seems like usually in plurals you don't see "le" with a word ending with "i". Mine was multiple choice translation answers. The correct choice didn't look right and another one wasn't plural "keys" so I picked what I thought was the logical one - "i chiavi" - I was wrong.
Most likely due to the origins of the word, which f.formica probably knows. Some words came from origins that don't necessarily follow general rules, others have been shortened and appear to break the rules--I think one such is la foto, which is actually shortened from "fotografia".
And never try to turn "foto" into a plural with a masculine ending. I'm told it's a very bad word.