Because step five is that we need to fill in our bonding electrons, and we start it with filling in two electrons per bond.

因为第五步要做的是将我们的成键电子填在这，所以我们开始在每个键处填上两个电子。

麻省理工公开课 - 化学原理课程节选

Now you start a process, a cyclic process, where the first step in the process is denaturing the DNA.

然后你就可以开始一个循环步骤,第一步是使DNA变性

耶鲁公开课 - 生物医学工程探索课程节选