Schuller, R. (1985). The be happy attitudes: Eight postive attitudes that can transform your life. Word books.
Dyfyniad Arddull ChicagoSchuller, Robert. The Be Happy Attitudes: Eight Postive Attitudes That Can Transform Your Life. Texas: Word books, 1985.
Dyfyniad MLASchuller, Robert. The Be Happy Attitudes: Eight Postive Attitudes That Can Transform Your Life. Word books, 1985.
Rhybudd: Mae'n bosib nad yw'r dyfyniadau hyn bob amser yn 100% cywir.