The correct answer is: D. a partner dies.
A partnership is a business relationship between two or more people who agree to share the profits and losses of the business. When a partner dies, the partnership is automatically dissolved. This is because the deceased partner’s share in the partnership is no longer owned by anyone. The surviving partners can choose to continue the business as a new partnership, but they are not required to do so.
The other options are not grounds for automatic dissolution of a partnership. A partner who misbehaves can be expelled from the partnership, but the partnership itself does not dissolve. A partner who becomes of unsound mind can be declared incompetent to manage their affairs, but the partnership can continue if the other partners agree. A business that is running at a loss can be dissolved, but this is not a requirement.
In conclusion, the only option that automatically dissolves a partnership is the death of a partner.