This helps because the plastic cover keeps the stamps off the wet air.

这是有帮助的，因为塑料盖使邮票远离潮湿的空气。

youdao

They could not provide adequate air cover for ground operations.

他们无法为地面作战行动提供足够的空中掩护。

《柯林斯英汉双解大词典》

The ships needed air cover once they reached enemy waters.

已到达敌方的水域，船只就需要空中掩护。

youdao