数学家研究纯数学不是因为它有用;他研究它是因为他喜欢它,他喜欢它是因为它美丽。
The journey of a thousand miles begins with one step.
中心地的等级反映了所提供的商品和服务的等级。
Sustainability is not just about planting trees; it's about planting the right trees in the right places for the right reasons.