sky是可数的，skies是指多片天空（银河系就有多片天空）。一般我们只用sky,指头上那片天空。
sky：n.天；天空；v.把(球)击向高空
第三人称单数： skies复数： skies现在分词： skying过去式： skied过去分词： skied
The stars were points of light in the sky.
天空中的点点光亮就是星星。
Several people described seeing strange lights in the sky.
好几个人都说看到天上出现了奇异光芒。
The sky suddenly went dark and it started to rain.
天空骤然转暗，随即下起雨来。
The sun was low in the sky.
太阳低挂在天空。
They saw the huge building outlined against the sky.
他们看见了在天空的映衬下那座巨大建筑的轮廓。
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