You create a new read-only table in the Dataverse database that has external data storage. 
What is the type of this table?

Answer options:

A.Standard
B.Relational
C.Activity
D.Virtual
E.System

Correct Answer: D 
Dataverse provides the three types of tables (entities): Standard — this is a usual custom table type that users can create. These tables store data and navigation for model-driven apps.
Activity — this is a special custom table type for storing activity information like appointments, phone calls, emails, tasks, etc.
Virtual — this custom table type has columns that bring data from external sources, like Azure SQL Database or Azure Cosmos DB.
Virtual tables have a list of limitations. There are two most important limitations: data in these tables are read-only, and users cannot create or update records. 
You need to use a classic interface for the creation of the virtual table. From the Power Apps portal, you can access Advanced settings, and then on the Administration screen, select Virtual Entity Data Sources. There you can create a new data source you would use for the virtual table creation (Number 2). 
Then from the Solutions/Default Solutions on the Power Apps portal screen, you can select the “Switch to classic” option. Portal will open the Dynamics 365 Default Solution screen. In the menu tree, you choose Entities and push the New button on the tab toolbar. 
You need to provide a name for the new table, check the Virtual Entity box (Number 1), and select a Data Source (Number 2). 

It is important to remember that you cannot change the table type after table creation. 
All other options are incorrect. 
For more information about Dataverse table types, please visit the below URLs: 

https://docs.microsoft.com/en-us/powerapps/maker/data-platform/types-of-entities
https://docs.microsoft.com/en-us/powerapps/maker/data-platform/create-edit-virtual-entities