nival line的用法和样例：
例句
- In north China, there are lots of lovely animals living above the snow line.
在北国的雪线上有很多可爱的小动物。 - This migration tends to stall near the snow line, where the gas headwind turns into a tailwind and provides an extra boost to the embryo's orbit.
这个迁移在接近雪线时会减缓下来，因为逆风气体在那附近将转成顺风，为胚胎轨道提供了额外的推力。
