• At the time,Irma was a single mother, working at every opportunity to support her four children.

    VOA: standard.2009.12.25

  • Remember, every time we have two electrons that are being shared, that's a single bond.

    还记得,每次我们有两个电子被共用,我们就有了一个单键。

    麻省理工公开课 - 化学原理课程节选

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