Phan says when shoppers see empty storefronts, it reminds them how tough the economic environment is and they feel less inclined to buy.

VOA: standard.2009.12.20

I'm going to give a name to that. And what you see there is I'm going to call divisors initially an empty tuple, something has nothing in it. Right here. And then I'm going to run through the same loop as before, going through this set of things, doing the check.

你们可以看到这里,我初始化一个空的元组,名为divisiors，这里，然后我会去运行,跟以前一样的循环，遍历这个集合内的东西,然后做检查，现在我要做的是，每次我找到了一个除数我要把它收集起来。

麻省理工公开课 - 计算机科学及编程导论课程节选

Keep in mind we do have this p orbital here and it's coming right out at us. And this p orbital is here, but it's empty, it doesn't have any electrons in it, that's why we don't have to worry about it in terms of getting our electrons as far away from each other as possible.

他们程120度角互相远离,这样它们离得最远，记住我们这里确实有个p轨道，它朝向我们，这里有个p轨道，但它是空的,里面没有电子,这就是为什么我们在考虑。

麻省理工公开课 - 化学原理课程节选