根据句意，补全下列各句所缺字母，注意要在空格上输入完整的单词

He's p_t_ing on his school cl_thes in his bedroom.

This story is about a young man. He worked hard at his lessons. He was too busy. He didn’t have time to rest, so he was ill. Every night, when he went to bed, he closed his eyes and tried to sleep（睡觉）. But he couldn't. He thought: “I must go to see the doctor.” He said to the doctor.
“I can't go to sleep at night.” “Try counting numbers. When you reach one thousand, you'll be asleep.”
The next day the man came back to the doctor's office. “Well,” said the doctor, “How are you today?”
“Yes, he said,” I tried counting one, two, three. . . up to（直到）one thousand. But when I reached five hundred and sixty-nine, I began to feel sleepy (感到困倦). I had to get up and drank some tea. Then I went on counting up to one thousand. But I still couldn't fall asleep.
【小题1】The young man couldn’t go to sleep because ________ .