So if you haven't clicked in yet, or if you want to change your answer, keep in mind that you might need to jot down, - for example, a Lewis structure before you can answer this question.

如果你还没有点答案，或者你想改变你的答案，记住你也许需要在回答问题前写点东西，比如画一画Lewis结构,来得到最终。

麻省理工公开课 - 化学原理课程节选