Final answer:
Mary must receive the consent of all of the partners in order to properly become a partner in the existing partnership.
Step-by-step explanation:
In order for Mary to properly become a partner with the existing partnership, she must receive the consent of all of the partners.
Under the Revised Uniform Partnership Act (RUPA), which governs general partnerships, it is required that all partners give their consent before a new partner can join the partnership.
Therefore, option c, Mary must receive the consent of all of the partners, is true in this case.