莱茵河流经瑞士、德国和荷兰，最终注入北海。

The ___Rhein flows through Switzerland, Germany, and the Netherlands before reaching the North Sea.

这种植物的根茎富含大黄酸，常被用作天然泻药。

The rhizome of this plant is rich in ___rhein, commonly used as a natural laxative.