you understand the rule you can do it well.A. ForB. AsC. OnceD. While

问题补充：

you understand the rule, you can do it well.

A. For

B. As

C. Once

D. While

答案：

A. For

B. As

(答案→)C. Once

D. While

解析： once连词，引导状语从句，一旦。