阅读材料，回答问题

材料一：近年来，我国多次出现大范围雾霾天气，多地PM2.5指数频临爆表，面对雾霾，很多百姓以“厚德载雾”，“自强不吸”，“霾头苦干”等词来调侃自己无奈的生存环境和表明战胜雾霾的信心，人民网网友“论霾”说：能否真正转变经济发展方式，如何进一步落实治霾各方责任，消除百姓“心肺之患”，人民翘首以盼。

材料二：今年两会报告指出：加大环境治理力度，铁腕治污是环境保护的关键，要有紧迫感和足够耐心，全面落实“史上最严”的新环境保护法，严厉打击各类环境违法行为，全面开展环境保护督查，强化督政问责。

结合上述材料，回答下列问题：

在数列$\left\{a_n\right\}$中，$a_{n+1}=a_{n+2}+a_n$，$a_1=2$，$a_2=5$，则$a_6$的值是  (    )

Weather Report

    Good morning everyone! Here is the weather report for tomorrow.

    It is cold in Beijing. It will rain，and there will be fog. You'd better wear your warm coat, a face mask and take an umbrella with you, if you go out.

    The weather in Sanya will be fine .It will be sunny and hot tomorrow. When you go out and enjoy the sunshine, please put on your sunglasses.

    It is hot in Xishuangbanna(西双版纳). And there will be a heavy rain in Xishuangbanna tomorrow. It will not be a good day for a trip, you'd better stay at home.

    It is windy and cold in Harbin（哈尔滨）. It will snowy. You should put on your warm coat and boots when you go out.

根据短文内容，选择正确答案。

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