According to the passage, the cattle help promote the growth of the wild

* Hướng dẫn giải

Đáp án là B. Ý trong bài: Cattle left outdoors to fend for themselves thrived on this hay. And the cattle themselves helped plant the fresh grass year after year for they trampled the natural seeds firmly into the soil to be watered by the melting snows of winter and the occasional rains of spring.