Translation:Are you sure?
I think DL ignores question marks (as I never include them and am still marked as right). Keeping that in mind, the only other way to know that you are saying "you're sure?" and not "you're sure" is inflection - which is only present in speech. Thus DL assumes that you are saying "you're sure". It is always better to be as clear as possible with DL, i.e. "Are you sure?" - even without the question mark it is clear that it is a question.
Is it a universal rule that "safe" doesn't come after "estar" or is that only the case when asking about a person's safety? I ask because #1 of the first entry at http://www.spanishdict.com/translate/seguro lists "Está más seguro en el banco" (It's safer in the bank). Why does this use "estar"? Are there other exceptions?
Best with Duo to play it straight and not try to become a Professional Translator right off the bat and just learn what the Spanish words mean without consideration of the often huge number of ways something can said in English. There's really no point in doing that to the neglect of focusing on what the Spanish words mean.
I'm still obviously learning here but from what I have learnt 'Está seguro? should be 'Are you sure? and 'Estás segura?' should be 'Are you secure?'. All I asked was why is my answer of 'are you secure?' wrong and you still didn't answer that... I just don't want to make bad habits. Estar and ser and all their forms seem to be somewhat important. Cheers.
Ah, I see the problem. "Seguro" and "segura" are the same word. There is no difference between them except gender. If you are talking to a male: seguro. If you are talking to a female: segura. ¨Estás¨ means ¨you are¨ (or ¨are you¨ in a question). ¨Está¨ means ¨he/she/it is¨ (or "is he/she/it" in a question). The way these are combined does not change the meaning of "segur@" (the @ indicates that it can be either gender, by the way. That little symbol can come in handy!)