"He needs a band-aid because he is bleeding."
Translation:Er braucht ein Pflaster, weil er blutet.
The goal of Duolingo, in my opinion, is to teach most commonly spoken language. In English I am most likely to hear Band-Aid than I am Bandage unless I am working as a medical professional. Also Band-Aid can no longer be enforced as a trademark because it has been over used. The same is for Klennex and Velcro.
I would recommend reviewing the Conjunctions section on Duolingo.