The correct hierarchical order is:
(3) Ad group
The top of the hierarchical order is Account because the first step before creating a Google Ad is creating an Account on Google Ads. Once you create your account, you can create an Ad campaign. Inside an ad campaign, you can create an Ad group that will contain multiple Ads. You can create one or multiple ads in one Ad group.
So, the correct hierarchical order is Account > Campaign > Ad Group > Ad
This question is a part of the Google Ads Search Certification Knowledge Check Assessment and the Check your knowledge exam of Explore the Value of Google Search lesson. You can find all the answers to both exams in our Google Ads Search Certification Knowledge Check Assessment Answers page, and Explore the Value of Google Search Answers page.