"My brother is an organic farmer."
Translation:Mon frère est un agriculteur bio.
I'm surprised you haven't seen this bug before. The Duolingo code allows for the "1" and "un" to be interchangeable because "un" is both an article and the spelled out numeral 1. Recall exercises in the "Numbers" skill: un, deux, trois, etc. You can pass those lessons by using digits: 1, 2, 3, etc. This coding leniency affects some of the presented answers throughout the course.