The ground is a box that is static, which Box2D knows, because the box has zero mass (by default) and therefore doesn't collide with other objects.

地面是一个静止的立方体，这是Box2D已知的，因为这个立方体的质量为零(默认)，因此不会与其他物体相撞。

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Only a handful of homes are zero-carbon, however, and many designs are too expensive to merit mass production

然而只有少数家庭是零排放，许多设计太过昂贵，不值得大量生产。

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But astronauts start losing muscle mass within days of entering a zero-gravity environment, and the longer they stay in space, the more their muscles shrink.

航天员在进入零重力环境的几天之内就开始出现肌肉流失。

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Nissan said the Leaf hatchback would be the world's first affordable, mass-produced, zero-emission car.

BBC: Nissan Leaf electric car to be built in Sunderland

Like all sales-driven organizations, Paramount needs to zero in quickly on the right executives, so forget about mass mailings.

FORBES: Wooing the customer