"You are a student."
When you have a positive "A is B" sentence and BOTH A and B are nouns, dash is required by Ukrainian punctuation conventions (except in come colloquial-style sentences and some special cases):
- Моя бабуся — письменниця.
- Мій друг — водій.
No dash is required when one of these is a pronoun (though one might still use a dash for emphasis):
- Це моя машина.
- Він водій.
Same in questions and negative sentences. No dash is usually there:
- Гаррі студент?
- Моя сестра не вчителька.
"Ти є студент."/"Ти є студентка." ARE both correct and ARE used in Ukrainian language today.
"Є" ('to be') is perfectly normal and accepted in today's Ukrainian conversation and writing. I do not know WHY Duolingo keeps marking the inclusion of the verb 'Є' ('буття'/'to be') as 'wrong', when it IS correct. This must be fixed.