以柳丝榆荚的从容反衬桃李的飘零，暗喻超然物外的态度

Sustainability is not an option; it's a responsibility we owe to future generations.

作家的生活是一种不断被打断的生活。

在互联网的世界里，最重要的是专注于客户体验。

The PAC learning framework provides a formal way to quantify the learnability of a concept class.