________ you understand the rule,you will have no further difficulty doing it.A.Though B.While C.Once D.Unless
问题描述：
________ you understand the rule,you will have no further difficulty doing it.
A.Though B.While C.Once D.Unless
答
答案C 四个连词比较,此题用once引导假设状语从句,表示“一旦你理解了这一规则”.查看原帖>>