"This recommendation is from our teacher."
Translation:Diese Empfehlung kommt von unserer Lehrerin.
I can think of two contexts for the English sentence: 1) The teacher recommended something to us (gave us advice). 2) The teacher wrote us a recommendation letter (recommended us to someone else). Can the German translation mean both?
"diese" is here in singular, because the word "Empfehlung" is a feminine, singular word (in nominative).
- masculine: Dieser Vorschlag kommt ... ~ suggestion
- feminine: Diese Empfehlung kommt ... ~ recommendation
- neuter: Dieses Ansinnen kommt ... ~ request, idea
- plural: Diese Vorschläge, diese Empfehlungen, diese Ansinnen kommen ...
That would be "The recommendation", not "This". Although the meaning is similar, it is not the closest possible translation so Duo sometimes doesn't accept these alternatives.
It should be accepted. Just note that you would also have to decline it in the masculine way, i.e. "von unserem Lehrer" vs. "von unserer Lehrerin".