The middle class is the real motor of economic growth.

中产阶级才是经济发展的真正动力。

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You might use this if you later changed your mind and decided to move motor back to the Vehicle class.

如果您稍后改变主意，决定还是把 motor 移回到 Vehicle 类中，那么您也许就会用到这种重构。

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Of greater significance, however, will be the new Mondeo-class 508, based on the graceful concept shown at last month’s Geneva motor show.

而意义更重大的，将是基于上月日内瓦车展上优雅的概念车型基础上开发的与福特蒙迪欧PK的508。

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Where a C-class motor from Estes puts out the equivalent of 2 pounds of thrust for one second, an H-class motor--the entry point to high-power rocketry--puts out 55 pounds.

FORBES: Serious Toys

Also more pleasing than any motor in this class is BMW's in-line six.

FORBES: Test Drives

A-class was unveiled at the Frankfurt Motor Show in September.

ECONOMIST: Car safety