必须找到新的能源，而这需要时间。

New sources of energy must be found, but this takes time.

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然而这需要时间，可人们往往缺乏耐心。

That will take time, however, and patience is in short supply.

youdao

而这需要时间，况且其约束力也不好保证。

But this could take time, and it is unclear how binding it would be.

youdao

These things run for variable amounts of time because they take input, a list of size of some amount.

而这一段的执行时间是可变的,因为它们需要输入一个包含一些元素的列表。

哈佛公开课 - 计算机科学课程节选