阅读下面短文，然后从所给的四个选项中选出一个最佳答案。

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    Reading            Step 1: Identify

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    TalkEnglish.com developed the "Click, Listen, and Repeat" functionality(功能). In most of the lessons, you read the sentence, click on the sentence to listen to the sentence, and then you can practice speaking by repeating after the audio file(音频文件) provided by a native English speaker. This method improves your reading, speaking, and listening all at the same time and makes learning English easy. You will improve your English speaking using this method.

如图，一次函数y₁=ax+b和y₂=﹣bx+a（a≠0，b≠0）在同一坐标系的图象．则 $\left\{\begin{array}{c}{y}_1=ax+b\\ y_2=-bx+a\end{array}\right.$的解$\left\{\begin{array}{c}x=m\\ y=n\end{array}\right.$中（　　）

已知|a|=2，|b|=5，且ab＜0，那么a+b的值为____