Because it tells the infinite affection of the sons and daughters of the motherland for the Yangtze River. The Yangtze River is the first river of the Chinese nation. Together with the ancient Yellow River, it nurtured and nourished the splendid civilization of the Chinese nation and became a symbol of our great motherland.

From "you feed children of all ethnic groups with sweet milk;" You hold up the mountains and the sea with strong arms. "

It can be seen that the author compares the Yangtze River to a mother, which shows that the Yangtze River has nurtured children of all ethnic groups and shows how broad-minded the mother of the Yangtze River is. The next sentence personifies the Yangtze River, which is very long, and compares it to the mother's strong arm, and holds the mountains and seas of the motherland in her hand, so that they can be closely connected and never separated.