一、创设情境,引入新课师:同学们,我们班的教室在几层?生:三层。师:可是有一次,吴老师从一层开始,一下上了三层的楼梯却找不到我们班,这是为什么?(全班学生迟疑了一会儿,随后纷纷举手)生:第一层没有楼梯,上三层只要走两层的楼梯。 First, the creation of situations, the introduction of a new class teacher: classmates, our class classrooms in several layers of Health: three. Teacher: But once, Mr. Wu started from the first floor, and once he got on the third floor of the stairs, he could not find our class. Why? (The students in the class hesitated for a moment, then raised their hands.) Students: The first floor did not Stairs, the three floors as long as two-story stairs.