他花了三年时间学习并通过了考试，终于成为一名注册会计师。

He studied for three years and passed the exam to become a licensed ___CPA.

这个广告活动采用按行动付费模式，只有当用户注册后才会收费。

This ad campaign uses a ___CPA model where advertisers are charged only after users sign up.