"The pelican has the apple."
Translation:Ο πελεκάνος έχει το μήλο.
Because ένα is the indefinite article, equivalent to 'a' - it could be any old apple. 'Το' is the (neuter) definite article, which is more specific. 'The' and 'a' aren't equivalent in English and they aren't in Greek either. Duo generally requires you to prove a reasonably specific translation, rather than a general interpretation, so that's why it was marked as incorrect.