Why does Salesforce require companies using Salesforce to have my domain subdomain in place? Choose 3 answers

Answer options:

A.Set up single-sign on (SSO) with external identity vendors
B.Set up authentication providers such as Google and Facebook so that users can log in to their Salesforce Org with their social account credentials
C.Use lightning components in lightning components tabs, lightning app builder, lightning pages and standalone apps
D.To create your own branding website

Correct Answer: A, B, and C 
Create your own subdomain for your Salesforce org to better manage login and authentication. With a subdomain, you can include your company name in your URL, for example, https://yourcompanyname.my.salesforce.com. You can also customize your login page, such as add your logo, change the color scheme, or add your own content on the right side of the login page. To create your own subdomain, you use the Salesforce Identity My Domain feature. 
References: 

https://developer.salesforce.com/docs/atlas.en-us.identityImplGuide.meta/identityImplGuide/domain_name_define.htm

Correct Answer: A, B, and C 
Create your own subdomain for your Salesforce org to better manage login and authentication. With a subdomain, you can include your company name in your URL, for example, https://yourcompanyname.my.salesforce.com. You can also customize your login page, such as add your logo, change the color scheme, or add your own content on the right side of the login page. To create your own subdomain, you use the Salesforce Identity My Domain feature. 
References: 

https://help.salesforce.com/articleView?id=domain_name_overview.htm&type=5