That male donkey became the father of the mule industry in the U.S.

那头公驴成为了美国骡子产业之父。

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A mule is the product of a horse crossed with a donkey.

骡是马和驴杂交的产物。

《牛津词典》

This is the tail of a mule.

这是骡子的尾巴。

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Mule stables dotted the route. But the canal company ran out of money as faster railroads stole most of their business, and the C&O Canal never reached Pittsburgh and the Ohio River.

VOA: standard.2010.04.29

A good example to keep in mind is the idea of a mule.

大家可以记住一个很好的例子，那就是骡子。

麻省理工公开课 - 化学原理课程节选

But the key moment, in the history of the mule, came a few years later, when there was a strike of cotton workers.

NEWYORKER: The Tweaker

Four or five mules long, a string is fashioned, each mule's halter tied to the rear of the next mule's aparejo.

ECONOMIST: New uses for an old pastime

Working in a two-man team, on opposite sides of the animal, packers sling a pair of manty-wrapped loads to the sides of a mule's aparejo and lay a 12-15-metre (40-50ft) lash rope gently across his creature's back.

ECONOMIST: New uses for an old pastime