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1Llyfrgan Ginzberg, Eli, 1911-“...Conservation of Human Resources Project (Columbia University)...”
Cyhoeddwyd 1967
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2Llyfrgan Ginzberg, Eli, 1911-“...Conservation of Human Resources Project (Columbia University)...”
Cyhoeddwyd 1968
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3Llyfrgan Ginzberg, Eli, 1911-“...Conservation of Human Resources Project (Columbia University)...”
Cyhoeddwyd 1971
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4Dogfen y Llywodraeth Llyfrgan Reubens, Beatrice G.“...Conservation of Human Resources Project (Columbia University)...”
Cyhoeddwyd 1981