Answer: D

Housing accumulation fund has the following properties: (1) universality. Urban employees, regardless of the nature of their work units, family income and whether they have housing, must pay the housing provident fund in accordance with the regulations on the management of housing provident fund. Therefore, option a is wrong. (2) Mandatory (policy). If a unit fails to register the deposit of housing provident fund or go through the formalities for the establishment of housing provident fund accounts for its employees, the housing provident fund management center has the power to order it to be handled within a time limit. If it fails to do so within the time limit, it can be punished according to the relevant provisions of the Regulations on the Management of Housing Provident Fund, and may apply to the people's court for compulsory execution. So option b is wrong. (3) welfare. In addition to the housing provident fund paid by employees, the unit should also pay a certain amount for employees, and the interest rate of housing provident fund loans is lower than that of commercial loans. Therefore, the C option is wrong and the D option is correct. (4) returnability. Workers retire, retire, or completely lose the ability to work and terminate labor relations with the unit, move out of the household registration or settle abroad, etc., and the paid housing provident fund will be returned to the individual workers.