"She used to be my friend."
Translation:Cô ấy đã từng là một người bạn của tôi.
Why is 'người bạn' rejected? It has been accepted elsewhere..'người bạn Phần Lan', for instance.
EDIT: in fact, it was marked right in the exact same sentence (given the Vietnamese, translate to English). So in one exercise, Vietnamese to English, it's required and if you don't have it it's marked wrong, and in another, if you DO have it it's marked wrong. DL's never-ending game of 'gotcha'.