Why can't leaves change colors, stay on their trees, and change back to green again when spring comes?

为什么树叶不能只是改变颜色，继续在树上生长，而当春天到来的时候再变回绿色？

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youdao

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They needed to change their flight path to take them around the moon and back toward Earth.

VOA: special.2009.07.22

Take your time. So, let's actually now take a 2-minute break, we're gonna change tapes and we'll come back and we'll actually write programs with a real computer and some real animated characters.

不急，现在休息2分钟，我们要换个录像带，一会再上课,等会开始写程序,构建一些动画人物。

哈佛公开课 - 计算机科学课程节选

and go back to change the laundry over and pick it up, and it's really a big pain. It's really awful.

然后走回去把衣服拿出来，真是太痛苦了，真的很烦人。

与众不同的纽约 - SpeakingMax英语口语达人

And as the technology becomes more ubiquitous and seamless, the chance for the nation to talk back and change the tone of debates is significant.

FORBES: Presidential Debates Get 'American Idol' Treatment: What That Means For The Future

Another man, age 53, decided to change careers and go back to a local college to study computer science.

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But during the spat, boatloads of Express Scripts customers shifted over to CVS Caremark ( CVS) and are unlikely to change back.

FORBES: Connect