下面是某位老师引入“负数”概念的教学片段。
师：我们当地7月份的平均气温是零上28℃，1月份的平均气温是零下3℃，问7月份的平均气温比1月份的平均气温高几度？如何列式计算？
生：用零上28℃减去零下3℃，得到的答案是31℃。
师：答案没错，算式呢？
生：文字与数字混在一起，一点也不美观。
生：零上28℃，我们常说成28℃，可用28表示，但是零下3℃不能说成3℃呀！也就不能用3表示。
师：大家的发言很有道理，如何解决这一系列的矛盾呢？看样子有必要引入一个新数来表示零下3℃。这时，零下3℃就可写成-3℃，-3就是负数。
问题：
（1）对该教师情境创设的合理性作出解释；
（2）在引入数学概念时，结合上述案例，说说教师创设情境要考虑哪些因素？
参考答案
参考解析
【分析题】
【分析题】
设计任务：请阅读下面学生信息和语言素材，设计一节20分钟的英语阅读课的教案。教案没有固定格式，但须包含下列要点：
●teaching objectives
●teaching contents
●key and difficult points
●major steps and time allocation
●activities and justifications
教学时间：20分钟
学生概况：某城镇普通中学高中一年级（第一学期）学生。班级人数40人。多数学生已经达到《普通高中英语课程标准（实验）》六级水平。学生课堂参与积极性一般。
语言素材：
Who am I?
Over time I have been changed quite a lot. I began as a calculating machine in France in 1642.
Although I was young I could simplify difficult sums.I developed very slowly and it took nearly two hundred years before I was built as an analytical machine by Charles Babbage. After I was programmed by an operator who used cards with holes,I could "think"logically and produce an answer quicker than any person. At that time, it was considered a technological revolution and the start of my "artificial intelligence". In 1936 my real father, Alan Turing, wrote a book about how I could be made to work as a"universal machine"to solve any difficult mathematical problem. From then on, I grew rapidly both in size and in brainpower. By the 1940s I had grown as large as a room, and I wondered if I would grow any larger. However, this reality also worried my designers. As time went by, I was made smaller. First as a PC(personal computer) and then as a laptop, I have been used in offices and homes since the 1970s.
These changes only became possible as my memory improved. First it was stored in tubes, then on transistors and later on very small chips. As a result, I totally changed my shape. As I have grown older I have also grown smaller. Over time my memory has developed so much that, like an elephant, I never forget anything I have been told! And my memory became so large that even I couldn't believe it! But I was always so lonely standing there by myself, until in the early 1960s they gave me a family connected by a network. I was able to share my knowledge with others through the World Wide Web.
Since the 1970s many new applications have been found for me. I have become very important in communication, finance and trade. I have also been put into robots and used to make mobile phones as well as help with medical operations. I have even been put into space rockets and sent to explore the Moon and Mars. Anyhow, my goal is to provide humans with a life of high quality. I am now truly filled with happiness that I am a devoted friend and helper of the human race!
