阅读下面短文，掌握其大意，然后从每小题所给的A、B、C、D四个选项中选出最佳答案。

    A professor( 教授) from New York University once went a remote area to do some science research(研究). One day, he ate something wrong and became sick, but it was too far to go to the city. "I have to see a doctor," he said to a local(当地人). "How can I be sure of getting a good one?"

     "It's easy," was the reply. "Every time a doctor loses a patient(病人), it's our law that he must fly a balloon above his office."

    So he began his search. One doctor flew 20 balloons, another 30. Then the professor found an office that was flying only five and went in.

    "You'll have to wait. I've been very busy," the young doctor told him. "I started my business only yesterday."