David was ill. He went to see a doctor. The doctor asked him to1 his tongue (舌头), and then he said, “ OK. You can put your tongue back now. There's 2 wrong with you, but I'm afraid you have a problem, you never take 3.”

    “But, doctor,” David said, “I don't think so.”

    “Don't 4me what you think,” the doctor said, “I see a lot of people 5you. None of them get any exercise. They sit in offices all day and in front of the TV in the evening. You must walk quickly for at least 30 minutes a day.”

    “Doctor, you don't understand, ”David said, “ I take enough exercise every day. ”

    “I don't want to 6 any excuses,” the doctor said, “You must find time7 exercise. If you don't, you will get8 and have health problems.”

    “But I walk every day.” David said.

    “Oh, yes, and I know what kind of walking that is. You walk9meters to the bus stop from your house, from the bus stop to your office, and from your office to your dining-room for lunch and back. That's not a real walk. I'm talking about a walk by the lake or in the park for 30 minutes every day. ”

    “Would you please 10 me, doctor?” David said, “I'm a postman. I walk for nearly seven hours every day.”

    For a moment the doctor was silent, then he said,“Can I see your tongue again?”