The standard library, that first line of code, it's not strictly necessary but any time you use a function, a tool that someone else wrote that lives in that so called library, you do need that include line as we'll see.

标准库函数--第一行代码，严格来说，不是每次都要写的，但是一旦你调用某个别人写，的函数，而这个函数又恰巧位于标准库里面,你就要像我们看到的这样，把它include进去。

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We should call it E-flat and put it up on the E line because there's kind of rule here that you have to use up each letter name in turn, each letter name in turn.

我们应该称之为降E,把它放在E的谱线上,因为这算是一个规则,要依次使用每个字母,依次用每个字母

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