Explanation/Reference:
Explanation:
Register-SPOHubSiteEnables the hub site feature on a site to make it a hub site.
SharePoint hub sites help you meet the needs of your organization by connecting and organizing sites based on project, department, division, region, etc. making it easier to:
discover related content such as news and other site activities,

apply common navigation, branding and site structure across associated sites,

search across all associated sites.

Incorrect Answers:
D: Set-SPOSiteGroupupdates the SharePoint Online owner and permission levels on a group inside a site collection.
References:
https://docs.microsoft.com/en-us/powershell/module/sharepoint-online/register-spohubsite
https://support.office.com/en-us/article/what-is-a-sharepoint-hub-site-fe26ae84-14b7-45b6-a6d1-
948b3966427f?ui=en-US&rs=en-US&ad=US