"Do you like that duck?"
Translation:Magst du die Ente?
This one is tricky since 'die' can also be a demonstrative adjective. (A use of the word a lot of learners don't seem to be aware of). If you stress the 'die', its meaning becomes equivalent to 'diese'. Whether it is wise for duolingo to include such subtleties in the exercices, I don't know. http://www.germanlanguageguide.com/german/grammar/demonstrative-adjective.asp