Each step of the double helix is a base made up of two kinds of nucleic acid.
Each step of the double helix is a base made up of two kinds of nucleic acid.
每阶二重螺旋线都是一个碱基，由两种核酸组成。
Each step of the double helix is a base made up of two kinds of nucleic acid.
每阶二重螺旋线都是一个碱基，由两种核酸组成。