从A、B、C、D四个选项中，选出可以填入空白处的最佳选项。
21. The rule can not be __________ every case.
A apply to B apply for C applied to D applied for
22. Only in this way__________ to make improvement in the operating system.
A. you can hope B. you did hope C. can you hope D. did you hope
23. I’ve lived in the south for over ten years. So I have been accustomed to _________ rice.
A eat B eating C ate D eaten
