完形填空。

    When Mary Smith was a 1, she wanted to be a teacher, 2 she liked children. When she was twenty, she began teaching in a small school. She was a good teacher, and she 3 a lot with the children in her class. They 4 her teaching.

    One day, 5 of the girls in her class said to her, "Miss Smith, 6 does a man's hair become grey before his beard (胡子)does?"

    Mary laughed(笑) and answered, "I don't know. Helen, do you know?"

    "I don't know, 7 . Miss Smith," said Helen, "But it happened 8 my father." The other children in the class laughed when they heard this.

    Then a boy said, "I 9, Miss Smith! A man's hair becomes grey 10because it's sixteen years older than his beard."