То ли я дурак, то ли лыжи не едут. Почему исправляет с "I am not AN engineer" на "I am not A engineer"? Может это какое-то исключение, что там не "an", а "a"? Ничего нигде не нашел.
Лыжи не едут!
Somebody didn't sleep enough when creating the exercise!
Thanks for commenting, fixed it.
P.S. Funnily tho, both versions were "accepted" translations there: "I am not an engineer" and "I am not a engineer". I have no idea why you got such a message, according to how Duo rolls both should've been accepted O_o (which is still wrong but)