旧公交车是造成城市污染的主要原因。

Old buses are major contributors to pollution in cities.

《柯林斯英汉双解大词典》

当然，侵蚀是造成其破坏的主要原因之一，但人类活动应承担的责任也越来越大。

Erosion, of course, is one of the key reasons for its destruction, but human activity is also increasingly responsible.

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这种细菌——存在于泥土和水中，而非粪便——是造成“游泳耳”的主要原因，症状是耳朵发痒疼痛和红肿。

This germ—which is present in soil and water, not feces—is responsible for "swimmers ear", an itchy or painful inflammation of the ear.

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