Which type of partnership involves at least one partner with unlimited liability?

The correct answer relates to the nature of partnerships and the liability of partners within different types. In a limited partnership, there must be at least one general partner who has unlimited liability, meaning they are personally responsible for all debts and obligations of the partnership. This structure allows for the presence of limited partners who contribute capital but have their liability restricted to the amount they invest, protecting their personal assets from business liabilities.

In contrast, an ordinary partnership typically involves all partners sharing unlimited liability, but the specific framing of the question emphasizes limited partnerships where the distinction between general and limited partners is crucial. The other types mentioned, like limited liability partnerships and separate liability partnerships, either provide limited liability protection to all partners or specifically isolate liability among partners, which is not the case in a limited partnership.