Are Business risk assessment definite requirement for Part A?

Short answer NO

SEE “approach to examining” in the published syllabus. Requirement for risk(s) could be business risk and/or audit risk/RoMM. Whereas audit risk/RoMM can be required without business risk you would not be asked for business risk alone – because it is RoMM that prompts the auditor’s response to assessed risks including the substantive procedures that will be a separate requirement of the same question.