In front of the platform, the students were talking with the professor over the quizzes of their ______subjects.
【正确答案】 A
【答案解析】解析：句意：在讲台前，学生们正在和教授讨论必修课的测验问题。指“必修科目，义务教育”时用compulsory(subjects，education)。compulsive强制的，强迫的。predominant支配的，主要的。