Backius巴基乌斯backn.后面；背脊；靠背；后背；后卫vt.支持；后退adv.向后地adj.向后的；后面的；偏远的；过时的；积欠的back coupling condition回授条件back-working distance背面工作距离backprojection operator反投影算子Backlight drive circuit背光驱动电路backness switching rule后舌性调整规则back shroud of impeller叶轮后盖板back-illuminated type背照明型back Du channel massage背部督脉推拿backed-up water level回水位back-wing penetration后排两边跟进

1. When water drops over a obstacle, it curls back on itself, forming a strong upstream current which may be capable of holding a boat or swimmer.
   当水跌过障碍物，它会自己回卷，形成一股强劲的可以困住船或者游泳者的回流。