九个数字选四个有多少组合

简介：In the early winter of Beijing's northern plains, there is a vast expanse of yellow land everywhere. The trees and weeds have all turned yellow. There is not a trace of life among the fields. There is only a large area of ​​corn stalks that have not had time to be harvested but have had their cobs removed. People were trampling and staggering, and they were swaying in the cold wind.