(1971). Helping others could be fun (Experimental ed.). Educational Publ. Bureau.
Citazione stile Chigago Style (17a edizione)Helping Others Could Be Fun. Experimental ed. Singapore: Educational Publ. Bureau, 1971.
Citatione MLA (9a ed.)Helping Others Could Be Fun. Experimental ed. Educational Publ. Bureau, 1971.
Attenzione: Queste citazioni potrebbero non essere precise al 100%.