A young man worked very hard at his lessons. He was too busy to have a rest. At last, he became ill, so he couldn’t go to sleep. Every night, when he went to bed, he closed his eyes and tried to sleep. But he always stayed awake and couldn’t fall asleep.
After some days, he decided to see a doctor.“I just can’t go to sleep at night. What should I do? Could you please help me?”
“I have a suggestion(建议)，”said the doctor. “Try counting numbers. By the time you reach one thousand, you’ll be asleep. I’m sure of it.”
The next day the man returned to the doctor’s office. “Well,” said the doctor, how are you today? Did you try my suggestion?”
The man still looked tired. “Yes,” he said, “I tried counting one , two, three—up to one thousand. But when I reached five hundred and sixty-nine, I began to feel sleepy. I had to get up and drink some tea so that I could go on counting up to one thousand. But then I still couldn’t fall asleep.”
【小题1】The young man couldn’t go to sleep because                       。