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种树的最佳时间是20年前,第二好的时间是现在。
The best time to plant a tree was 20 years ago. The second best time is now.
埃尔德什差异问题让我着迷,因为它陈述起来如此简单,但含义却如此深刻。
The best way to predict the future is to create it.