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.

Yinsen: That does n't look like the Jericho missile .
Tony Stark: That 's because it is a miniaturized arc reactor . I 've got a big _ one _ powering my factory at home .
Yinsen: What will it generate ?
Tony Stark: If my math is right - and it always is - three gigajoules per second .
Yinsen: That could run your heart for fifty lifetimes !
Tony Stark: Yeah ... or something big for fifteen minutes .
reactor