Clear the air:

打扫空气 ×

改变困境 缓解紧张状态 √

例句：

I think making concession is a good way to clear the air.

我觉得缓解紧张气氛最好的办法是让步。

I dare say:

我敢于说 ×

我想 很可能 √

例句：

I dare say you know about it already.

你大概已经知道了

Freshwater:

新鲜的水 ×

淡水 √

例句：

China has the world's richest freshwater fish resources.

中国淡水鱼资源居世界之首。