Authorities say they quickly killed two of the gunmen, but two others continued to fire machine guns in the extended battle in Pul-i-Alam, Witnesses say U.S.military helicopters were part of the response force, and one aircraft fired a rocket into a multi-story building which the insurgents had seized, used to launch their attack and had rigged with explosives.

VOA: standard.2009.08.10

During development of the embryo it goes from being a single cell, the fertilized egg, to being a multi-cellular organism with billions of cells in it.

胚胎的发育,始于一个单一细胞,即受精卵,直到形成一个以十亿计数量的细胞构成的,多细胞有机体

耶鲁公开课 - 生物医学工程探索课程节选

During development of the embryo it goes from being a single cell, the fertilized egg, to being a multi-cellular organism with billions of cells in it.

胚胎的发育,始于一个单一细胞,即受精卵,直到形成一个以十亿计数量的细胞构成的,多细胞有机体

耶鲁公开课 - 生物医学工程探索课程节选