Tannins from the skins and sometimes stems of grapes and the oak barrels used for aging cause the bitter or astringent aftertaste in some red wines.

在一些红葡萄酒中，葡萄皮、葡萄梗和熟成用的橡木桶所带来的单宁会给人带来苦味或收敛性的感觉。

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Rhizobia establish a symbiotic relationship with their host plant ― exchanging nitrogen for nutrients ― by forming nodules, which penetrate the roots and sometimes stems of the plant.

根瘤菌通过形成根瘤和它们的宿主建立了一种共生关系——用氮换取营养。 根瘤通常会渗透进植物的根，有时候还会渗透进植物的茎。

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But, sometimes, that fatigue stems from low iron stores, particularly prevalent among women in their 20s and 30s, who don’t eat much meat.

但有时身体缺铁会导致疲劳。 特别是20岁至30岁的女性，由于少食肉类，这种现象尤为普遍。

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