Exam MS-203 topic 1 question 22 discussion

Your company has a Microsoft Exchange Server 2019 hybrid deployment.
Users in the advertising department and the editorial department of the company have mailboxes in Exchange Online.
A company policy requires that the advertising department users and the editorial department users be segmented based on the following requirements:
✑ The advertising department users must not see the editorial department users in the global address list (GAL).
✑ The editorial department users must not see the advertising department users in the GAL.
✑ The editorial department users must be treated as external recipients of the advertising department users.
✑ The advertising department users must be treated as external recipients of the editorial department users.
You need to recommend a solution that meets the requirements and minimizes costs and effort.
What should you recommend?