Mulla, M. A., & Upshur, J. (1979). Aptitude, attitude, motivation, anxiety, intolerance of ambiguity and other biographical variables as predictors of achivement in EFL by high school science major seniors in Saudi Arabia. University of Michigan.
توثيق أسلوب شيكاغو (الطبعة السابعة عشر)Mulla, Mohammed Amin, و Jack Upshur. Aptitude, Attitude, Motivation, Anxiety, Intolerance of Ambiguity and Other Biographical Variables as Predictors of Achivement in EFL by High School Science Major Seniors in Saudi Arabia. Michigan: University of Michigan, 1979.
توثيق جمعية اللغة المعاصرة MLA (الطبعة الثامنة)Mulla, Mohammed Amin, و Jack Upshur. Aptitude, Attitude, Motivation, Anxiety, Intolerance of Ambiguity and Other Biographical Variables as Predictors of Achivement in EFL by High School Science Major Seniors in Saudi Arabia. University of Michigan, 1979.