I happen to be a customer of PetroChina. . . China Oil and Gas Co., Ltd. no longer writes about the branch behind North China Natural Gas. As far as I know, there is a requirement for PetroChina to publish publications, that is, regular publications. Therefore, as a customer of this company, I always look for cheap ones around 400 yuan. As long as the publishing department can find it and then go online, they all admit it, regardless of Wanfang or VIP.