Mr. Robinson worked in Africa.His son was born there. His name was John.

 One winter Mr. and Mrs. Robinson went to England，and they took John there. John was seven years old then.One day it snowed.The boy went into the garden，and he played in the snow. He said，“Snow is very beautiful，but it is very cold ”Then he said，“What is this? It is a big，round piece of glass. It is beautiful，but it is very cold，too. ”But it was not glass. It was ice. It was on a bucket (桶)of water.

 John said，“Who puts this glass here? I am going to take it into the house. ”He took the ice to his father and said，“This is a beautiful piece of glass，but it is very cold and wet. It was on a bucket of water in the garden. ”Mr. Robinson smiled and said，“Take it to the kitchen，put it in front of the stove there，and dry it. ”The boy took the ice to the kitchen and put it in front of the stove. He dried his hands，because they were very cold and wet，and then he went to the ice again. He looked at it，and then he took it to his father again. He said，“I put this glass in front of the stove，but it does not get drier. It becomes wetter and smaller. ”

 John didn’t know what the ice was，because().