与早期的软件开发方式相比较，结构化周期法最重要的指导原则应该是( )。
A．自顶向下设计
B．分阶段开发
C．逐步求精
D．用户需求至上
参考答案：D
---Who could have imagined that Barack Obama, a black boy brought up by his white grandparents, would become the President of the USA?
---Well, I don’t think it any wonder. ______.
A．Birds of a feather flock together.
B．Like father, like son.
C．Every dog has its day.
D．The early bird catches the worm.
经营单位应当建立易制毒化学品销售台账，销售台账和证明材料复印件应当保存几年备查
A．5年B．4年C．3年D．2年E．1年
