It is well known to all that water, enough, can change into ice quickly．
A. if cooling
B. though to be cooled
C. when cooled
D. when is cooled
网友回答
A. if cooling
B. though to be cooled
(答案→)C. when cooled
D. when is cooled
解析：考查状语从句的省略。句意：我们都知道，当水足够冷却，很快就会变成冰。应用when cooled，中间省略了it is ，所以选C。