古希腊哲学家说:“一个人不能两次踏进同一条河流。”与此同理,一个教师即使是执教同一内容也不可能两次踏进同一课堂。课堂永远处于千变万化的动态中,它要求教师运用教学机智,针对偶然事件,巧妙出奇地处理,实现教学目标的动态生成。课堂教学既是科学,又是艺术。当前在许多地区,普遍实行集体备课,教师在新课标理论的指导下,共同研究教材, The ancient Greek philosopher said: “A person can not step into the same river twice.” "By the same token, a teacher can not even enter the same class twice even with the same content. The classroom is always in the ever-changing dynamic, requiring teachers to use teaching tactics, for accidental events, cleverly and surprisingly, to achieve the dynamic generation of teaching objectives. Classroom teaching is both science and art. In many areas at present, the collective practice of class preparation is generally practiced. Under the guidance of the new curriculum standard theory, teachers jointly study teaching materials,