Salim AL-Kutubi , Hadeel, and Inaam Razzaq AL-Saiq. “On Student Comprehension For There Year Courses In Mathematics Department”. University of Thi-Qar Journal of Science, vol. 1, no. 3, Jan. 2009, pp. 64-103, http://mail.jsci.utq.edu.iq/index.php/main/article/view/187.