法国大革命被认为是一场真正的政治大革命。这场革命爆发的标志是(   )

某化学兴趣小组的同学做粗盐提纯实验，如图是同学们作粗盐提纯的实验示意图．

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命题“若$f\left(x\right)$是奇函数，则$f\left(-x\right)$是奇函数”的否命题是(      )

    Scientists say life will be very different in 2050.

    First，there will be no TV channels（频道）in 2050.People will choose a program from a computer and watch it on TV.In 2050，we will get information from the computers only.

    Second，water will be a big problem in 2050.In many places，people won't have water to drink.

    Third，cars will use new and clean fuels and they will go very fast.There will be a computer in every car.And the computers will control the cars and there won't be any accidents（事故）.