它们占据了非常小的一部分，但当我们考虑原子的构造的时候，不用考虑它们会占用很多的质量。
They take up a teeny bit, but when we're thinking about the set up of the atom, we don't have to account for them as using up a lot of the mass.
但是，我们已经把这些困难的部分提出了，所以你不用担心了。
Naturally though, we've put the hard yards in so you don't have to.
如果您无法完成余下的任务，也不用担心 —— 本系列的第 3 部分将帮助您完成这些任务。
And don't worry if you can't complete the pending tasks -- Part 3 of this series will help you do just that.
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