Definition: 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.
Input: Penelope Garcia:  I have gone through every frequency and wavelength and , and I haven't been able to pick up on anything !
Kevin Lynch: Well , just slow down .
Penelope Garcia: I 'm frustrated
Kevin Lynch: I get that . Let 's just go back . You 've checked audix ?
Kevin Lynch: Yes
Kevin Lynch: All right , Nady systems , AKG , Electro - Voice , VocoPro ?
Penelope Garcia: Yes , yes and yes . Gone through all every frequencies in the freaking northern hemisphere , and nothing !
Kevin Lynch: I do n't know , I mean these are the only frequencies that are above ground
Penelope Garcia: Wait ! Underground !
Kevin Lynch: No , I said : above ground
Penelope Garcia: ELF ! Extremely Low Frequency . It 's the only _ one _ that can penetrate underground Got a hit You 've lipstick on your face

ELF