Open University. (1986). Open Learning. Longman Group.
Citação do estilo Chicago (17ª ed.)Open University. Open Learning. Essex, Inglaterra: Longman Group, 1986.
Citação MLA (8ª ed.)Open University. Open Learning. Longman Group, 1986.
Rhybudd: Mae'n bosib nad yw'r dyfyniadau hyn bob amser yn 100% cywir.