1.To get the main idea of the text by skimming the key words,and accurately judge the source of the article according to the content of the text.

2.To find out the main details quickly in the text through intensive reading,and clear the causal logic of the text.

3.To learn the background,purpose and way of the monarch??s migration,understand the influence of human behavior on their survival,and deepen the cognition of the text and the theme of the unit.