关系数据库是 (14) 的集合,其结构是由关系模式定义的。
A.元组
B.列
C.字段
D.表
参考答案:D
治疗应首选
A.青霉素
B.先锋霉素
C.异烟肼
D.链霉素
E.利福平
It is necessary that we should spend one hour _____ English every morning. [ ]
A. practice to read
B. practice reading
C. practicing reading
D. practicing to read