You will be given a definition of a task first, then some input of the task.
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.

General K'Vagh: Fleet Admiral Krell will not extend his deadline .
Dr. Phlox: The only possible way to get results on Krell 's schedule is to infect four healthy Klingons .
General K'Vagh: You have four right here !
Dr. Phlox: Only one of these strains will work , the other _ three _ will be lethal . Ethically , it 's unthinkable !
General K'Vagh: The ethics , Doctor , are simple : three lives to save millions .
Output:
strains