Given the task definition, example input & output, solve the new input case.
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 _. There are several possible answers, you'll need to choose the proper one. Carefully read the given text, pay special attention to the marked number, think about what (unwritten) information the marked number holds inside, choose the most adequate word(s) from the optional answers. If none of them seems right to you, there's also an option for other. If your answer is "REFERENCE", also write the reference entity, otherwise write the implicit option name. Options to choose from are:
REFERENCE: Some object which is being mentioned in the text before or after the target number. The reference answer has a higher priority than any other. If both Reference and another answer are possible, prioritize the Reference.
YEAR: Describing a calendric year
AGE: Describing someone's age
CURRENCY: Reference to some monetary value e.g dollar, euro etc.
PEOPLE: Describing a single/plural persons
TIME: Describing a time of the day. Usually you can add the word o'clock after those numbers.
OTHER: Some other option, which isn't listed here.
Example: Jess Mastriani: No, I don't want another crooler, thank you very much.
 FBI Agent Nicole Scott: But it's good for you. It's got... honeyglaze. Please die for this crooler, Jess.
 Jess Mastriani: I've had _ two _ already. Who eats three croolers in a night? 
FBI Agent Nicole Scott: Take a look. [Nicole takes a huge bite] Mmmmm, Mmmmm, Mmmmm!
Output: REFERENCE crooler
In this example, the number two refers to something that appears in this text. In this example, it refers to the word: crooler.

New input case for you: 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 !
Output:
REFERENCE silos