在数据库系统中完成数据库的定义、操纵和维护工作的是 【9】 。
参考答案：DBMS和数据库管理员
— What do you think of your new English teacher?
— She was well prepared for her first lesson and left us a good ______. [ ]
A. expression
B. instruction
C. appearance
D. impression
低闪点类、中闪点类、高闪点类易燃液体分别是如何划分的？
