一项有关“18岁时,你最想做的事是什么?”的调查显示,70%的青少年“想拥有一间真正独立的房间”。这表明青少年特别渴望维护自己的(　　)

    Mr. Brown lived in a house less than two miles from his office, so he was able to drive home every day for lunch. Every time he drove home at noon, he found many cars were parked outside his house and there was no room for his own car. He had to drive somewhere else to park his car. Then he had to walk back home. This made him very angry.
   He had put up a board, which said, “ No parking” in the garden facing the road, but nobody noticed it. People seemed to obey(遵守) only a police notice with letters on a blue board:
POLICE NOTICE
NO PARKING
   Mrs. Brown suggested that he could steal a police notice. He was afraid to do so. She then suggested that he could make one just like a police notice. He said he was not the police and couldn’t use the word “police”. Several days later, Mr. Brown made a blue board with white letters:
POLITE NOTICE
NO PARKING
   “ Oh!” Mrs. Brown said, “You told me you weren’t going to use the word  “police”, but why do you use it now?” “Really?” he asked, “Look again.” She started to laugh. “You are really clever.”