Endorsements: How Sports Stars Get Inside Your Head by Dan Peterson (January 12, 2009) livescience.com Malcolm Bird, The Complete Guide to Business and Sales Presentation.
Bản gốc lưu trữ ngày 31 tháng 7 năm 2012.  ^ Endorsements: How Sports Stars Get Inside Your Head by Dan Peterson (January 12, 2009) livescience.com Malcolm Bird, The Complete Guide to Business and Sales Presentation.