There are cells within your body that are always in the process of division and forming new cells, and sometimes this is for a tissue where cells only have a finite lifetime.

你体内的一些细胞,始终在不断分裂,并生成新的细胞,很多时候,是在一些细胞寿命有限的组织中

耶鲁公开课 - 生物医学工程探索课程节选

So if you get the CD set, not only do you get a wonderful beginning library of classical music but in effect you get a lifetime service contract with it.

所以一旦你买了整套CD,你不仅可以拥有一个古典乐图书馆,而且还可以享受终身服务

耶鲁公开课 - 聆听音乐课程节选