Word missing in one of the test anwers

Question

She knows this girl who plays guitar. It should be ----THE guitar

Cécile Janty-Davies · Accepted Answer

Hillary, 
Having carried out some research and discussed with some members of the team, this is what I found -
" Both versions are grammatically correct and can be used in English, but they have slightly different meanings:
1. "This is the girl who plays guitar" - This implies that the girl generally plays guitar as an instrument or skill. It doesn't refer to a specific guitar.
2. "This is the girl who plays the guitar" - This version, with "the" before guitar, can imply either:
a) She plays a specific guitar that has been previously mentioned or is known in context.
b) She plays the guitar as an instrument in general (similar to the first version, but slightly more formal).
Both forms are commonly used and often interchangeable in casual conversation when referring to playing an instrument.
Anne, these are our guidelines for the English we use -
https://www.kwiziq.com/is-this-english-correct
 
I hope this helps!

Anne Davies · Answer

I’d say that "plays guitar" is American English and "plays the guitar" is British English - the former construction is creeping into the UK media eg he plays piano, but it isn’t necessarily regarded as grammatical English here!

I’d be interested to know the general policy of the language experts on this site vis à vis usages from the UK/US/other Anglophone countries.