Wastewater and backflow from fracking adds up to 1 trillion gallons a year.

水力压裂产生的废水和回流每年总计达 1 万亿加仑。

The chambers are separated by valves that prevent the backflow of blood as it moves through the heart.

这些腔室由瓣膜隔开，防止血液在心脏中流动时回流。

The ureters insert into the bladder at the ureterovesical junction at a sideways angle so that when the bladder becomes full, it compresses the openings to the ureters preventing the backflow of urine.

输尿管在输尿管-膀胱交界处倾斜插入膀胱；这样一来，当膀胱充盈时，输尿管开口受压，从而阻止尿液反流。

If those valves leak, or a vein experiences too much pressure, the backflow of blood can stretch and twist the vein, leaving you with varicose veins, or if this happens in another part of the body, hemorrhoids.

如果这些瓣膜泄漏，或者静脉压力过大，血液回流会拉伸和扭曲静脉，留下静脉曲张，或者如果这种情况发生在身体的另一个部位，就会长痔疮。