It could be sawdust or agricultural waste like grain hulls, cocoa or coffee shells.

VOA: special.2009.06.22

So coffee and the milk and whatever you like in your coffee would be the system.

么咖啡，牛奶以及任何你能想到的,在你的咖啡里的东西就是一个系统。

麻省理工公开课 - 热力学与动力学课程节选

So coffee and the milk and whatever you like in your coffee would be the system.

么咖啡，牛奶以及任何你能想到的,在你的咖啡里的东西就是一个系统。

麻省理工公开课 - 热力学与动力学课程节选