Located in tropical areas at low altitudes, savannas are stable ecosystems, some wet and some dry consisting of vast grasslands with scattered trees or shrubs.

"热带稀树草原位于热带地区，海拔较低，是一种稳定的生态系统，由广阔的草地和稀疏分布其中的树木或灌木组成，有些地区湿润，有些地区干燥。

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Bailey agrees Lippl's findings are interesting but laments the study's lack of a control group staying at low altitudes.

贝利也认为利普的发现很有趣，但遗憾的是实验没有在低海拔地区设置对照组。

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Only small aircraft, and those needing tough low-speed propulsion at low altitudes, for agricultural work and fire-fighting, still have piston engines.

只有一些小型的飞机，以及那些用于在低空低速爬升飞行的用于农业以及灭火用途的飞机仍然使用活塞发动机。

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At low altitudes they help to cool the Earth by reflecting sunlight away from it.

ECONOMIST: Climatology: Grey-sky thinking | The

The scenery belies the relatively low altitudes, with great alpine hiking at just 2, 000m above sea level.

BBC: Spain��s mountains made of cheese

They are most effective when fired at aircraft flying at low altitudes, as at take-off or landing.

ECONOMIST: The shoulder-held threat | The