Talk about your experiences and interests in combination with your actual situation. For example, I chose this topic mainly because I am particularly interested in this paper. I don't think it is easy for college students to write their graduation thesis.
If the topic of graduation thesis is too big or too difficult, it will be difficult to complete the writing task; On the other hand, the topic is too easy, the scientific research ability can not be well exercised, and the purpose of writing graduation thesis can not be achieved. Therefore, choosing a topic with appropriate difficulty and size can ensure the smooth progress of writing.