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.

Let me give you an 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!
The answer to this example can be: REFERENCE crooler
Here is why: In this example, the number two refers to something that appears in this text. In this example, it refers to the word: crooler.

OK. solve this:
Penny:  You are a grown man . Haven't you ever been sick before ?
Sheldon Cooper: Of course . But not by myself .
Penny: Really ? Never ?
Sheldon Cooper: Well , once , when I was _ fifteen _ and spending the summer at the Heidelberg Institute in Germany .
Penny: Studying abroad ?
Sheldon Cooper: No , visiting professor . Anyway , the local cuisine was a little more sausage - based than I 'm used to , and the result was an internal blitzkrieg , with my lower intestine playing the part of Czechoslovakia .
Answer:
AGE