Once you set the rotor size, you pretty much have determined the thrust air speed (if you know the mass of the helicopter).
一旦旋翼大小固定，几乎决定了空气推进速度(如果你知道直升机重量)。
With high-speed trains, people will set up factories and business centers in the west once and for all.
有了高速火车，人们可以一次性在西部建立工厂和商业中心。
With high-speed trains, people will set up factories and business centers in the west once and for all.
有了高速火车，人们可以一次性在西部建立工厂和商业中心。
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