Não informado. (1969). Industrial and Commercial Training. J. Wellens, Industrial and Technical Training.
Παραπομπή σε μορφή Chicago (17η εκδ.)Não informado. Industrial and Commercial Training. Guilsborough, Inglaterra: J. Wellens, Industrial and Technical Training, 1969.
Παραπομπή σε μορφή MLA (8th εκδ.)Não informado. Industrial and Commercial Training. J. Wellens, Industrial and Technical Training, 1969.
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