题型:填空题 We may find that learning a foreign language does not have to be________learning our mother tongue,but can in fact be twice ________.A.twice as hard as;as easy asB.as twice hard as;as easyC.twice as hard as;as easyD.as twice hard;as easy as 查看答案
题型:填空题 已知学生关系S(学生,姓名,班级,课程名称,成绩),学号由入学年份、专业编号和班内编号组成。则其候选关键字是______。A.(学号,姓名) B.(学号,课程名称)C.(姓名威绩) D.(学号,班级) 查看答案