In fact, the first, second, and third buying and selling points can all be classified as the first type of buying and selling points, just at different levels. So why not talk about the first type of buying and selling points, because this will involve different levels, which is equivalent to looking at it with microscopes of different levels at the same time, which is too messy, and it is even more messy in actual use, because the meanings of buying and selling points at different levels are different, so we have to study them at one level, so that there are three types of buying and selling points.
