Interviewers often ask this question to ascertain your work experience, how you handle multiple things and your perception about the job.

You should stress upon depicting that there is no typical day for a BA and how varied your work is, through the day. Show your rich experience by explaining how you responds to the emails, meeting with the subject matter experts, clarification of the business flow to the technical team, discussion with the project manager over the project status, preparation and review of functional documents.