Final answer:
Membership into Beta Sigma Phi is strictly by invitation only, requiring an endorsement from a current member for new members to join. Option a is correct.
Step-by-step explanation:
Membership into Beta Sigma Phi is by invitation only. Beta Sigma Phi is an international women's social, service, and cultural organization. To become a member, one must be invited by an existing member, underscoring the exclusive nature of its membership policies.
Unlike some organizations that may allow members to apply or be nominated, Beta Sigma Phi maintains a policy where prospective members can only join through a personal invitation, highlighting the importance of current member endorsement in the selection process.