"There is blood on the ticket."
Translation:На билете кровь.
Actually, I think they are both equally 'correct.' The one Duolingo has chosen, "На билете кровь?", is the standard version of the sentence, this version emphasises the word blood. That there is something on the ticket is already known, the new information is blood.
I believe "Кровь на билете?" puts an emphasis on the words на билете, i.e. it emphasises that the blood is possibly on the ticket and not somewhere else. The information that there is blood somewhere is not treated as new or important, the important or new information is on the ticket.
"Кровь есть на билете?" is also correct but it puts an emphasis on the words 'there is', i.e. the existens of the blood in the present tense is important to differentiate between that and "Кровь было на билете"?
As for "Есть кровь на билете", I am not so sure. I think it is correct and does the same thing as the previous sentence but weaker in some sense, i.e. there is a small emphasis on there is, kind of like "Is there blood on the ticket?".
Please note that I am not a native speaker of Russian, the information I am giving you maybe slightly wrong. Native speakers, feel free to correct me.
EDIT: I have came back after reading an article about word order in Russian and I have edited some stuff above. ^^ I also want to add, that if you really want to emphasise the word is and construct a sentence like 'I there really blood on the ticket?', you would say "Кровь на билете есть?". In Russian, old information is always put in the beginning of the sentence and new information at the end.
If you are wondering which article I read, it was this the one entitled 'A guide to Russian word order' by Серая жаба (in Belarusian, Шэрая жаба). Here's the link: http://goo.gl/hH9EfE.
[Side note: You can also use the particle ли to mark a question, this particle is then placed after the old information. So, for this sentence, it would be "На билете ли кровь?". From what I am told by Серая жаба, it conveys exactly the same meaning as the version with out the particle ли.]