阅读下面短文,根据所给情节进行续写,使之构成一个完整的故事。An 80-year-old man was sitting on the sofa in his house along with his 45-year-old highly educated son．Suddenly a crow perched on their window．The father asked his son, What is this？The son replied, It is a crow．After a few minutes, the father asked his son for the second time, What is this？The son said, Father, I have just now told you, it's a crow!After a little while, the old father again asked his son for the third time, What is this？At this time some expression of irritation was felt in the s