Não informado. (1969). Industrial and Commercial Training. J. Wellens, Industrial and Technical Training.
शिकागो शैली (17वां संस्करण) प्रशस्ति पत्रNão informado. Industrial and Commercial Training. Guilsborough, Inglaterra: J. Wellens, Industrial and Technical Training, 1969.
एमएलए (8वां संस्करण) प्रशस्ति पत्रNão informado. Industrial and Commercial Training. J. Wellens, Industrial and Technical Training, 1969.
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