Selk, J. (2018). Executive toughness: The mental-training program to increase your leadership performance (Updated edition.). McGraw-Hill Education.
توثيق أسلوب شيكاغو (الطبعة السابعة عشر)Selk, Jason. Executive Toughness: The Mental-training Program to Increase Your Leadership Performance. Updated edition. New York: McGraw-Hill Education, 2018.
توثيق جمعية اللغة المعاصرة MLA (الطبعة الثامنة)Selk, Jason. Executive Toughness: The Mental-training Program to Increase Your Leadership Performance. Updated edition. McGraw-Hill Education, 2018.
تحذير: قد لا تكون هذه الاستشهادات دائما دقيقة بنسبة 100%.