"We hear with the ears on our head."
Translation:Vi hører med ørene på vores hoved.
"Ørerne" and "ørene" are both valid here, and accepted by Duolingo, I'd imagine which one you use depends on where you are in the country. In Zealand "øren" is sometimes used as the plural form, and so "ørene" is the best definite form to use, whereas in Jutland, øren isn't used as the indefinite plural form at all, and it's always "ører" and "ørerne"
Having lived all my life on Zealand, I'd add that I've never heard anyone use "øren" in any way except the word "ørenlyd", which isn't too common in itself. If anyone used "øren" as a plural of "øre", as a native Dane I'd look at them weird.
On the other hand, while I'd probably spell it "ørerne" myself, I doubt I would be confused by "ørene" and might not even notice.