看，这就是加减号的敏感性。
最近一封信，他索性把加减号都写好，我只要划掉一个就行。
In the last letter he simply wrote out a plus and a minus sign, and I was supposed to cross one out.
按照惯例，通常使用向右的三角形取代closed，向下的三角形取代open；也可使用加减号，加号表示closed，减号表示open。
By convention, these graphics are usually triangles that point to the right for closed or down for open; or plus and minus signs, where plus means closed and minus means open.
蜜蜂会做加减法——它们用颜色来代替加号和减号。
Bees are capable of addition and subtraction — using colors in the place of plus and minus symbols.
蜜蜂会做加减法——它们用颜色来代替加号和减号。
Bees are capable of addition and subtraction — using colors in the place of plus and minus symbols.
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