challenge: What is the primary condition for Hajós's theorem to hold in a finite abelian group?
  
  A. The group must be expressed as the Cartesian product of sets of prime cardinality
  B. The group must be expressed as the Cartesian product of cyclic groups
  C. The group must be expressed as the Cartesian product of simplexes containing the identity element
  D. The group must be expressed as the Cartesian product of subgroups of prime order
  Answer: 