D. Proceeds of disposal of fixed assets

Explanation:

The proceeds of disposal of fixed assets refer to the cash generated from selling off a company’s fixed assets, but it is not typically considered a source of financing. Financing sources are usually related to obtaining funds through loans, credit, or equity, such as bank overdrafts, short-term loans, suppliers’ credit, and operating leases. The sale of assets is a one-time transaction, not a recurring financing option, making option D the correct answer.