a) A partnership.
Explanation:
A partnership occurs when two or more entities jointly manage a business and share its profits. In contrast, a joint venture involves two or more parties collaborating, pooling resources to achieve a particular objective. A sole proprietorship denotes a single owner who retains all profits and bears unlimited liability, while a limited liability company restricts liability to the invested amount for its members. Given these details, it's evident that the law practice established by Mike and Steve is classified as a partnership due to their shared control and profit-sharing arrangement.
