Lean on the ball as shown, keep the back flat or maintain its natural curve, with the legs straight.

身体俯卧于球体之上，动作如图所示。背部保持正直或保持自然弯曲状态，腿部伸直。

youdao

The neat streets of Oslo are not a natural setting for crime fiction. Nor, with its cows and country smells, is the flat farming land of Sweden's southern tip.

奥斯陆整洁的街道并非犯罪小说里常有的环境，而且那些奶牛和乡村味道会告诉你，这里只是瑞典最南端的平坦农田。

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That reflects some natural advantages (the place is mostly flat) and some deliberate decisions (such as plenty of cycle lanes and places to lock up bikes).

这其中既有天然优势（牛津这个地方地势较为平坦）的因素，也有正确决策的功劳（比如兴建了许多自行车道以及锁车的地方）的结果。

youdao

The most natural,straightforward,literal,flat-footed interpretation.

最自然，直接，理性和踏实的解释。

耶鲁公开课 - 死亡课程节选

People knocked flat by natural disasters deserve support from citizens who've had no such misfortune.

WSJ: Henninger: Hurricane Christie

Special light boxes, or flat lamps that simulate natural white light with a blue tint, are also effective, noted Foster, who has been consulting with Delta on the feasibility of introducing such lights into airport lounges.

BBC: Online calculators combat jet lag

Wright's Prairie Homes contrasted the grand edifices of the Chicago School with their modest low-slung horizon lines, flat roofs, overhanging eaves, unadorned open spaces and natural materials that mirrored the Midwestern landscape.

BBC: The infamous architecture of Chicago