高一英语题-today is very cold ,isn't it?-yes,the river is ___over

高一英语题
-today is very cold ,isn't it?
-yes,the river is ___over.
Afreezed Bfreeze Cfrozen Dfreezing
答案是C
和这一题比较一下：
without the air ,the earth at night____,too cold for us to live.
Awould be freezing cold.
Bwill be freezing cold
Cwould be frozen cold
Dcan freeze coldly
答案是A.
我就是不懂freeze的用法,以前没学过,但又有这样的题,请讲解一下freeze的用法,谢谢.