It's kinda tough to blindly guess "glaesi" when the other options fit grammatically just as well
Thank you for pointing this out; it's now been fixed. All of these errors that occur throughout the course arose from the fact that I believed that users would be given an English translation and then asked to choose the right form. You can see how I thought exercises like this would be fine if you had an English translation to work with. Slowly I'm going through and finding all the bad ones and fixing them, but it's not like I have a list of them anywhere. I need users to report them so I know they're there.