Norback, C. T., & Norback, P. G. (1979). The must words: The 6000 most important words for a successful and profitable vocabulary. McGraw-Hill.

Norback, Craig T., and Peter G. Norback. The Must Words: The 6000 Most Important Words for a Successful and Profitable Vocabulary. New York: McGraw-Hill, 1979.

Norback, Craig T., and Peter G. Norback. The Must Words: The 6000 Most Important Words for a Successful and Profitable Vocabulary. McGraw-Hill, 1979.