flying levels

例句：

1. 1. The plane is flying at a level that allows for comfortable travel.
   飞机以一个适宜的飞行高度飞行，使得旅行舒适。
2. 2. The pilot had to adjust the plane's altitude to avoid obstacles.
   飞行员不得不调整飞机的高度以避免障碍物。
3. 3. The astronaut was flying at an altitude of 100 kilometers above the Earth'ssurface.
   宇航员在距地球表面100公里的高空飞行。