Nowadays it's believed that the largest contributors to air pollution are gasoline vehicles. They not only give off harmful gases but also dangerous and heavy metal particles（微粒） that can result in environmental dangers. We can't stop using vehicles and thus stop air pollution right away. However, at least we can look for better replacements so that air pollution can be reduced. According to studies, hydrogen （氢）cars prove to be a better replacement for traditional cars.

    A hydrogen car is a vehicle that uses hydrogen as fuel for its engine to work. There are two types of hydrogen cars. The first one is to use hydrogen as a fuel, and the second one is to use hydrogen fuel cells（电池） to provide power for the car. Hydrogen and oxygen react chemically with each other to produce electricity, thus starting the car.

    There are many advantages of hydrogen cars. For example, hydrogen is available in plenty. Therefore, you needn't worry about a lack of hydrogen. More importantly, no harmful gases are released as by-products .The only by-products are water and a little amount of heat so air pollution is prevented up to a large extent.

    However, there are also some problems with hydrogen cars. For instance, in case of damage, the cost of repairing and replacing fuel cells is high. Worse still, hydrogen is a material which can burn easily, so it can result in a huge explosion of the car.

    The concept of hydrogen cars is relatively new for most people. Research is still in progress to reduce disadvantages and increase advantages. Therefore, hydrogen cars are expected to contribute their bit towards making this planet better and healthier!

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①对于任意的x∈R，都有f（x）=cos （2x﹣ $\frac{2\pi }{3}$ ）；

②对于任意的x∈in R，都有f（x+ $\frac{\pi }{2}$ ）=f（x﹣ $\frac{\pi }{2}$ ）；

③对于任意的x∈R，都有f（ $\frac{\pi }{3}$ ﹣x）=f（ $\frac{\pi }{3}$ +x）．

其中，全部正确结论的序号是____．

某地铁自开通以来，发展速度不断加快，现已成为市民主要出行方式之一，2016年地铁安全运输乘客约381万乘次，用科学记数法表示381万为（   ）