It's a waste of money not to take any training courses. Science, physics, chemistry, biology and mathematics. Chemistry is the simplest, and it is called the liberal arts in science. As long as you remember more, you can get high marks. Biology is basically a backrest. Physics only needs to remember and understand a few laws and do many problems. Mathematics is actually not that terrible. Junior high school mathematics is not a unitary linear equation, a binary linear equation, and there is no circle. First of all, we must clarify the basic concepts, and then remember one thing: change with the same. In a problem, you analyze constant factors. This constant factor is the key to solving the problem!