问题
选择题
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
答案
答案：C
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。