When do you know when to use "sua" instead of "teu"
When is it appropriate to use 'teu' and 'tua'?
When it is related to "tu"
http://www.duolingo.com/comment/294129
Why is it not 'A sua chave' please?
It's also right.
But I have a question, I wrote "Seu chave" and it hasn't been correct. is it correct or not? Thanks.
It's not correct. "Chave" is a feminine noun, so you should use "sua".
Seu is in case of words with artikel "o".
It is not correct
Could I have written Tua chave and been correct?
Yes, it is also right.