请认真阅读下面各题，从题中所给的A、B、C、D四个选项中，选出最佳选项，并在答题卡上将该项涂黑。
21. Below the topsoil of the earth is the subsoil, _____ layer that contains stones mixed with a small amount of _____ organic matter.
A. a; the B. the; the C. 不填; 不填 D. a; 不填
22. Usually the teachers will be busy ________ the test papers after an examination.
A. grading B. naming C. ranking D. grouping
23. Through the open window we saw on the floor the happy father lying ________ his stomach, his daughter riding excitedly on his back.
A. on B. with C. above D. from
24. With everything arranged properly, the project is sure
