I've been spending lots of time on these two and now I can tell the major from minor at ease. thanks a lot!

I've been doing well so far but got stuck at interval comparison exercise 18 (telling harmonic major 3rd from minor 3rd). I do melodic intervals with no problem. Initially I was stuck with harmonic 2nds but now I can tell them apart with esae. Now the problem is harmonic 3rds. I really have no idea ...