Most Decembers are wet and rainy.

大多数十二月都是潮湿多雨的。

It was one of the coldest Decembers ever.

这是有史以来最冷的十二月之一。

I had seen this kind of situation too, but that would normally happen in the late Decembers.

蝴蝶漫山遍野的情景，自己也有见过，但是这样的情况，通常在十二份才出现。