This term we have a new teacher of English. His name is Mr. Peterson. He is an Australian. He is not very tall and he is thin. He has a round face and small blue eyes. He wears glasses and they make him look smart. He has dark brown hair.

      Mr. Peterson works very hard. In class, he has many good ideas to make the class very interesting. We all like his class. After class, he always encourages us to speak more English. Sometimes, he plays games with us. He is very strong and he can play basketball and football very well. He is good at sports. Sometimes he plays table tennis with us, but he doesn’t play it very well.

       Mr. Peterson loves living in China very much. He enjoys lots of things in China. He really loves eating Chinese food. He loves traveling in China too. He is going to visit Xi’an next month.

提示词：suggestion, pronunciation, perform

提示问题：

    When and where will you prepare for the program?

    How can Tom get there?

    What can Tom do for you?

Dear Tom,

    How is it going?

    I am writing to invite you to help us prepare for the school English Talent Show.

    I am looking forward to your early reply.

Yours,

Li Hua

阅读下列材料，结合所学知识回答。
对历史人物的评价摆脱不了政治环境的影响。综观国共关系史，随着两党关系的演变，共产党对蒋介石的评价也有不同。自西安事变以后，共产党对蒋介石的态度逐渐发生变化，特别是1937年到1945年期间。如：1938年在延安六届六中全会上，***就说过“国民党历史上有两个伟大的领袖，第一个是孙中山，第二个是蒋介石”。1945年。共产党也公开表示，“承认蒋先生的领导，承认蒋先生在全国的地位。”但是，在1946年到1949年期间，共产党对蒋介石的态度又发生变化，斥之为“人民公敌”、独夫民贼”。还有大众流传的“蒋该死”、“蒋匪帮”之类，就是那个时期出现的。
问题：
（1）分别结合1937年到1945年以及1946年到1949年的主要史实，简要分析共产党对蒋介石评价高低的变化及原因。
（2）你认为评价历史人物的基本原则是什么？

下列化学用语与含义相符的是（　　）