Should I use American or British spelling in the Listening test?

In the IELTS Listening test, both British and American forms of English are accepted as correct. 

This means that using the American spelling of a word is fine, and that using the British spelling is also fine.

For example, if the correct answer is 'city centre', you could write this as 'city centre' (BrE) or as 'city center' (AmE).