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.

Special Agent Seeley Booth: From now on when one of us has been shot at , has to tell the other _ one _ right away
Dr. Temperance 'Bones' Brennan: Okay , unless one of us is already dead
Special Agent Seeley Booth: Right !
us