Partner by estoppel is a

Partner with limited power
Nominal partner
Sleeping partner
Partner under special situation

The correct answer is: D. Partner under special situation.

A partner by estoppel is a person who is not a partner in a partnership but is held out by the partners as being a partner, and who is therefore estopped from denying that they are a partner. This can happen, for example, if a person is introduced to clients as a partner, or if they are given a power of attorney on behalf of the partnership.

A partner with limited power is a partner who has agreed to have their powers limited. This can be done, for example, by a partnership agreement. A nominal partner is a partner who is not involved in the day-to-day running of the partnership, but who is still liable for the debts of the partnership. A sleeping partner is a partner who is not involved in the day-to-day running of the partnership, and who does not have any liability for the debts of the partnership.

I hope this helps!