单选题 Mrs. Jones gave music lessons at school. She had a good voice and enjoyed singing, ex- cept that some of her high notes(音符)sounded like a gate that had been forgotten to oil(上油). Mrs. Jones knew that so well that she tried to practice these high notes if she was free. As she lived in a small house, she usually had to go for long walks along the country roads and practiced high notes there. Every time she heard a car or a person coming along the road, she stopped and waited until she could no longer be heard before she started practicing again.
One afternoon a car came up behind her so fast that she didn't hear it until it was only a few meters from her, She was singing some of her highest and most difficult notes at that time when the car passed. The driver stopped his car in front of her, suddenly jumped out and began to look at his car carefully. To his great surprise, he couldn't find anything wrong with his car. He got back into the car and drove off.