what's wrong with simple?
Reporting it. According to wiktionary, simple and sencillo are synonyms.
Exactly! Why not translate "simple" as "simple", or "básico"? Are they saying that sencillo = simple = básico? No difference?
Used hover to check the spelling of argumento. Instead of argumento, the hover hint was discusion. But that was marked wrong.
Por qué no "está sencillo", teniendo en cuenta que el argumento podría ser temporal.
Duo also accepts "El alegato es sencillo."