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.
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Question: The Doctor:  Those shields wo n't hold them there for long .
Briggs: They 'll last until we 're back to Earth .
The Doctor: And then ?
Briggs: There 's only a few of them : our security men will cope with them .
The Doctor: They 're an invasion force , Earth is where they want to go . There are considerably more than a few on board .
Adric: How many of these silos are you carrying ?
Briggs: Oh , _ fifteen _ thousand or ...
Briggs: No
Briggs: . It 's not possible !

Answer: silos


Question: Lt. Reed:  All we have left is to reset the emitters .
Lieutenant Talas: What 's the frequency ?
Lt. Reed: I 'll do it .
Lieutenant Talas: You do n't trust me .
Lt. Reed: No offence , but when it comes to our weapons frequencies , I would n't trust my own mother .
Lieutenant Talas: Is your mother considered a security risk ?
Lt. Reed: It 's just an expression .
Lieutenant Talas: An odd _ one _ . My mother 's security clearance is higher than mine .

Answer: expression


Question: Master Sergeant Ernest G. Bilko:  Hey , Paparelli , how are those tickets going for the Meet Stormin ' Norman barbeque ?
Paparelli: It 's a sellout , Sarge .
Master Sergeant Ernest G. Bilko: Did you find a lookalike ?
Paparelli: We found _ one _ .
Master Sergeant Ernest G. Bilko: Ahh . No wonder they call me a Master Sergeant .

Answer:
lookalike