直线 zhíxiàn HSK5 straight line Origin Definitions Defs Strokes Stroke Words Sentences Sents 垂直线 chuízhíxiàn vertical line 异面直线 yìmiànzhíxiàn skew lines (math.) skew lines直线加速器 zhíxiànjiāsùqì linear accelerator 直线性加速器 zhíxiànxìngjiāsùqì linear accelerator