This is not necessarily true! There was an original logistics major in our school who did not reply and handed in his graduation thesis directly. However, undergraduates usually defend themselves. Actually, there's nothing to defend. At that time, our teacher asked several questions about your graduation thesis. Some questions can be found in the thesis, and some questions need to be improvised, but most of them can't escape your major. Other teachers will ask questions about the shortcomings in your paper. But there is nothing wrong. Defense is just a form.