四、单项填空（共15分，每小题1分）
从下列各题所给的A、B、C、D四个选项中，选择可以填入空白处的最佳选项。
21. Mary is very friendly. I like to study with __________.
A. she B. her C. hers D. herself
22. I got good grade in the PE test __________ May 11th.
A. on B. in C. at D. for
23. Our teachers________ very kind and patient, so we love them very much.
A. am B. is C. are D. be
