BELL, F. Ground engineer-s reference book. Butterworths.
शिकागो शैली (17वां संस्करण) प्रशस्ति पत्रBELL, F.G. Ground Engineer-s Reference Book. Butterworths.
एमएलए (8वां संस्करण) प्रशस्ति पत्रBELL, F.G. Ground Engineer-s Reference Book. Butterworths.
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