Translation:When the traitor enters the city, immediately kill him!
I tried entering When the traitor enters the city, immediately kill [him / her], but I didn't have a him or a her. but I did have a he. So I tried changing it up, *When he enters the city, immediately kill the traitor", but that wasn't accepted. I guess this is one case where they actively prevent me from following sentence order.
These discussions are linked to sentences, not particular exercises, so you have to tell us more about what kind of exercise you had problems with. It sounds like you may have had a tile exercise. For other types of exercises, you get a report option of "my answer should have been accepted", which is very helpful for us, but I think doesn't get offered to users on tile exercises. There were some variations missing from the accepted answers. I have added them now, but it may take a day or two for the system to update. Hopefully the changes will make the tile exercise easier and more straight forward.