文化现象存在于社会生活的方方面面。下列属于文化活动的是(　　)

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    Mr. Black is American, but he is in Canada now. He is a tall man with funny glasses. He works in a big city but lives in a town far away. He lives on the twentieth floor of a building. Every morning he gets up early. Then he gets into the lift and it takes him down to the first floor. He runs to the bus stop and catches the early bus. It usually takes him about two hours to get to the factory by bus. Then he gets off the bus and walks into the workshop(车间) quickly. He starts his work at eight in the morning.

在点燃条件下，4.4gC₃H₈与12.8gO₂恰好完全反应，生成7.2g水，4.4g二氧化碳和agX，则a的值为____；该反应的化学方程式为：____．

高￥考^资@源*网下列提法符合上题哲学道理的做法有

若{a_n}为递减数列，则{a_n}的通项公式可以为（  ）