5.3 is a classic material, with two versions: penny number and mathematical number. If you look closely, you will find that another reason for the different colors is the different versions. You must buy the latest version now! I just bought a Wang Houxiong, which is white and thick, except that the teacher asked me to buy it. Usually, in addition to being a teacher, I will also selectively make my own books, which feels very beneficial. This year's college entrance examination, I learned math 130+