F,文中说This had penetrated from the surfaces of the rocks into the cracks. However,... snow has not melted in the TM in recent times。 had penetrated 说明过去渗透过 snow has not melted in recent times 现在雪没有融化。缺少moisture不能渗透. 那么之前为什么能渗透呢。因为之前温度高于freezing。 所以F是正确的