In this task, you will use your knowledge about language (and common sense) to determine what element the marked number refers to. The numbers are marked with two underlines around them, like: _ number _. Your answer should be chosen from the given text, and should not contain other words.

Commander Sisko: No need to ask how you 're doing .
Major Kira: Chasing after ghosts !
Commander Sisko: You have twelve hours to catch _ one _ .
Major Kira: And then ?
Commander Sisko: People start dying .
ghosts