教师启发学生进行自觉概括的最常用方法是______。
参考答案：鼓励学生主动参与问题的讨论
The elderly need special care in winter, as they are _____ to the sudden changes of weather. [ ]
A. sensible
B. flexible
C. sensitive
D. positive
简述ISO9000系列标准的结构。
