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1LlyfrCyhoeddwyd 1975“...Open University (Great Britain). Faculty of Educational Studies...”
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2Llyfrgan Fowler, Gerald“...Open University (Great Britain). Faculty of Educational Studies...”
Cyhoeddwyd 1973
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3LlyfrCyhoeddwyd 1979“...Open University (Great Britain). Faculty of Educational Studies...”
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4LlyfrCyhoeddwyd 1977“...Open University (Great Britain). Faculty of Educational Studies...”