Share capital, debentures, and retained earnings are all sources of finance, but in this case, the question is specifically asking for a source of short-term finance. Out of the given options, only one is a source of short-term finance, and that is "debentures." Debentures are bonds or other types of debt securities issued by a company that are repayable within a short period, usually a few years or less. Therefore, debentures can be considered a source of short-term finance for companies. Corporate tax, on the other hand, is a type of tax paid by companies on their profits and is not a source of finance for them.