Please select all correct statements about the alternate keys.

Answer options:

A.An alternate key is a GUID
B.An alternate key uniquely identifies a Dataverse record
C.An alternate key is only for integration with external systems
D.An alternate key can be a unique combination of columns

Correct Answers: B and D 
All Dataverse tables have a primary key. A primary key is a GUID. When you read or write records, it is not efficient to search for GUID first and then access the record. Therefore, it is more convenient and efficient to have another unique key for the record — an alternate key. You can use any column or combination of columns that uniquely identify the records as an alternate key. An alternate key can be used as a substitute for a primary key. An alternate key is also helpful for integration between Dataverse records and external sources. External databases can use an alternate key for the records access. Options B is correct because an alternate key is a unique identifier of the Dataverse record.
Options D is correct because an alternate key can be a column or combination of columns that uniquely identifies the Dataverse record.
Options A is incorrect because an alternate key is an alternative to the GUID of the primary key.
Options C is incorrect because users can use an alternate key to access the records within Dataverse and integrate with external databases.
For more information about Dataverse alternate keys, please visit the below URLs: 

https://docs.microsoft.com/en-us/powerapps/developer/data-platform/define-alternate-keys-entity
https://docs.microsoft.com/en-us/powerapps/maker/data-platform/define-alternate-keys-portal