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.
Q: Danny Messer: Mac , is this him , the scumbag that killed Aiden ?
Det. Mac Taylor: Danny , get out of here .
Danny Messer: Just let me talk to him . Aww . I will get him to crack , I promise you that .
Det. Mac Taylor: How ? By tuning him up ? Stella 's got the case , she knows what to do !
Danny Messer: This is Aiden ! She 's one of our own , Mac !
Det. Mac Taylor: That 's why we ca n't make any mistakes . We do this _ one _ by the book , understand ?
Danny Messer: Alright , I just wanted to help .
Det. Mac Taylor: I know , me too
A:
case