You manage an Office 365 tenant that uses SharePoint Online. The organization purchases a second domain name to use with SharePoint Online.
You need to create a new site collection that uses the new domain name.
Which two actions can you perform? Each correct answer presents a complete solution.

A.
From the SharePoint admin center, add and configure the domain.

B.
From the SharePoint admin center, rename the site collection by using the new domain.

C.
From the Office 365 admin center, add and configure the domain.

D.
From the Office 365 admin center, configure the Global Administrator user principal name to use the new domain.

Explanation:
B: Create a Public Web Site by using a custom domain name
1. Go to SharePoint Online Administration Center and Click ‘Site Collections’.
2. Click ‘New’ button and Click ‘Public Website’.
3. Create your Public Website. At the URL, choose the custom domain name you want to use as a SharePoint Public Website address.
C: The New-MSOLFederatedDomain cmdlet, part of Office 365, adds a new single sign-on domain (also known as identity-federated domain) to Microsoft Online

Services and configures the relying party trust settings between the on-premises AD FS server and Microsoft Online Services.
How to add a custom domain name in SharePoint Online with a federated domain environment
http://blogs.technet.com/b/ptsblog/archive/2012/06/25/how-to-add-a-custom-domain-name-in-sharepoint-online-with-a-federated-domain-environment.aspx