Onions are biennials; their life cycle is two years long.

VOA: special.2011.06.28

Most of you have probably at some point or another learned about the cell cycle, or the process of a cell going from being a single cell to being two cells.

大部分人应该或多或少,学过细胞周期,就是细胞,一分为二的过程

耶鲁公开课 - 生物医学工程探索课程节选

The cycle of Newtonian dynamics has two parts.

牛顿动力学体系由两部分组成

耶鲁公开课 - 基础物理课程节选

If you start with only one, you have two pieces of DNA, then you'll get 2 to the Nth fragments after N cycles because each cycle you're doubling the number.

如果你从仅仅一个DNA开始,你有两条DNA链,经过N次循环后,就得到二的N次方个DNA片段,因为每次循环都使其数量翻倍

耶鲁公开课 - 生物医学工程探索课程节选