Translation:The distance is greater than a kilometer.
I got what you mean. My confusion is because of the another example. Actually wider would be better for that example instead of longer, isn't it? https://forum.duolingo.com/comment/23030523/Το-κρεβάτι-είναι-μακρύτερο-από-το-τραπέζι
No one can see the answers users submit. If you are certain the answer you gave has been omited from the accepted alternatives, you have checked it to be grammatically correct and the spelling is right, please report it using the REPORT button and then "My answer should be accepted".