To this day coal is said to be screened in the colliery when it has stone and other impurities removed from it.
据说煤中掺有石子和其它杂质须去掉时，至今仍得把煤在矿上筛过。
2
Using coal gangue of Qitaihe as raw material, the best surface medication agent was screened through the test of medication choosing and rubber filling.