根据首字母和所给英文释义，填写单词。

1. r________: a competition in speed (速度)

2. o________: to do what a law or a rule says

3. a________: to be successful in doing or finishing something by trying hard

4. i________: the quality of being very important

5. s________: to gain sth or reach an aim

预防术后切口感染使用抗菌药物的最佳时间是（）。

A.术前3天给药

B.术前0.5～1小时

C.术前6小时给药

D.术前1天给药

E.术后回病房即给药