Every university professor has experienced the test of time and many years of such teaching activities, and then his knowledge has been greatly improved before he can be promoted to the position of professor through corresponding certification, because a professor is not a position, but a professional title. Every professor can say that there is no problem in knowledge. They all reach the peak of this knowledge in their own good chat, so they may be hard in teaching activities, but they will not encounter such a big academic problem, because they may teach master students or doctors. Basically, there are not many undergraduate professors.