阅读短文，从每题所给的A、B、C和D四个选项中，选出最佳选项。
Bill is a good boy. He is seven years old, and he likes going to school. But he cannot get up early.
He always wakes up until (直到) nine or ten o'clock in the morning.
His mother doesn't want him to be late for school, so she buys an alarm clock for him. She says to Bill, "You must get up when you hear the clock ring." "Yes, Mum," Bill answers. From then on, when he hears the clock ring at six o'clock in the morning, he gets up quickly.
One day his mother forgets to wind up (上发条) the clock. And the next morning, Bill doesn't get up on time. It's time for breakfast, so his mother goes to wake Bill up, Bill is in bed and his eyes are open. "Why don't you get up?" his mother asks, "You tell me that I must get up when I hear the clock ring, so I am waiting for the clock to ring," Bill said.