The only way to learn mathematics is to do mathematics.

At SF Express, we not only provide courier services, but also a sense of trust and peace of mind.

解释：河流川泽中有污水，深山草野中藏有瘴气，美玉也有微小的瑕疵。

In the food industry, trust is the most important ingredient you'll ever work with.

There is no man, however wise, who has not at some period of his youth said things, or lived in a way the consciousness of which is so unpleasant to him in later life that he would gladly, if he could, expunge it from his memory.