One summer night Ludwig Beethoven took a walk in the suburb   of Bonn. Suddenly a gentle wind came. He heard some music. He listened carefully and found it was his F sonata. He followed the music and came to a small house. There through the window, he saw a girl playing a very old piano and a young man was making shoes beside her, he pushed the door open and went in. The host received him very warmly and told him that the girl was his sister, who was blind but very fond of music. They couldn't afford to send her to a master.  So she was only trying to play some music she heard the neighbors play. She knew it was the work of a great composer. Beethoven was very much moved. Suddenly the candle was blown out. Moonlight struck on the girl's slender figure. Then Beethoven played music for them. He played so wonderful that the brother and sister were amazed. That was his famous Clair de lune. The girl couldn't go to the teacher most probably because  _  .
she was blind her brother didn't want her to go they were too poor good friends