According to the different writing contents and words, there are generally three ways to add cases to papers. Small papers can generally be directly listed as an introduction or the first question. As a separate part, the introduction is written as a paragraph. As the first part, it cannot exceed three paragraphs, and the number of words is generally between 300- 1000 words. If it is a graduation thesis, it is usually placed after theoretical and conceptual analysis, which is the second or third part. According to the actual situation, this generally accounts for about 10% of the words in the full text.