a. Trade Credit: This is a common source of finance for sole proprietors. It allows businesses to buy and pay for goods later, thus improving cash flow.
b. Overdrafts: Banks provide a facility that allows a sole proprietor to withdraw more money than is available in their account, providing short-term financing.
c. Debentures: These are a type of long-term debt instrument typically used by corporations to raise capital. Sole proprietors do not issue debentures, as they are not structured as corporations and usually cannot raise funds in this way.
d. Leasing of Equipment: This is a way for sole proprietors to obtain the use of equipment without having to purchase it outright. Leasing provides access to necessary assets while managing cash flow.


In summary, debentures are not a source of finance for sole proprietors, making option C the correct choice.