You create a Dataverse environment without a database. 
Please select all security roles that you can assign to the users of this environment.

Answer options:

A.System Customizer
B.Environment Maker
C.System Administrator
D.Environment Admin
E.Basic User

Correct Answers: B and D 
When you create a Dataverse environment without a database, you have only two security role choices: Environment Maker and Environment Admin. Environment Maker can create new resources, like apps, flows, connections, gateways; share the apps with the users in an organization. But this role does not have privileges to access the environment’s data.
Environment Admin can perform all administrative tasks in the environment, like add and remove users from Environment Maker or Admin roles; provision Dataverse database, and view and manage the environment`s resources.
Option A is incorrect because System Customizer is a Dataverse security role for the environments with the Dataverse database.
Option C is incorrect because System Administrator is a Dataverse security role for the environments with the Dataverse database.
Option E is incorrect because Basic user (previously Common Data Service User) is a Dataverse security role for the environments with the Dataverse database.
For more information about Dataverse security roles, please visit the below URL: 

https://docs.microsoft.com/en-us/power-platform/admin/database-security