“稻花香里说丰年，听取蛙声一片”，这里的蛙声是谁发出的？有何意义？（　　）

阅读理解
Henry was from the United States and he had come to London for a holiday.
One day he was not feeling well.  So he was to the clerk at the desk of his hotel and said, “I want to see a doctor. Can you give me the name of a good one?” The clerk looked in a book, and said, “Dr. Grey.”
“Is he expensive?”
“Well,” the clerk answered, “he always asks for his patients two pounds for their first visit to him, and 1.5 pounds for later visit.”
Henry decided (决定)  to save 50 pence. When he went to see the doctor he said, “I’ve come again, doctor.”
For a few seconds the doctor looked at his face carefully without saying anything. Then he nodded and said, “Oh, yes.” He examined (检查) him and then said, “Everything’s going as it should do. Just continue (继续)with the medicine (药) I gave you last time.”