1. The sky was covered in nimbostratus clouds, signaling an approaching storm.
天空被层云覆盖，预示着暴风雨即将来临。

2. Nimbostratus clouds are known for their thick, dark appearance and ability to produce prolonged periods of rain.
层积云以其浓密的外观和长时间的降雨能力而闻名。

3. The nimbostratus clouds hung low in the sky, casting a gloomy shadow over the landscape.
层积云低悬在天空中，给景观投下了阴沉的阴影。

4. As the nimbostratus clouds moved in, the temperature dropped and the wind picked up.
随着层积云的移动，气温下降，风势加大。

5. The nimbostratus clouds eventually gave way to clear skies and sunshine.
层积云最终被晴朗的天空和阳光取代。

6. Pilots are trained to navigate through nimbostratus clouds using their instruments to avoid dangerous weather conditions.
飞行员接受过训练，可以使用仪器穿越层积云，以避免危险的天气条件。