3 topics of discussion (interview survey) (maths applicant)

Does anyone (especially maths applicants) have any idea on the choosing 3 "topics of discussion"? It says that "interviewers will probably only use one of the topics at interview". Can anyone provide me some example answers? Surely I have distinct areas of interest that were included in the personal statement, but I'm just not sure how to format the answers and how it will affect the interview questions.