A company needs to store 2 TB worth of data that is infrequently used. The data needs to be accessed via Power BI. Which of the following could be used as a cost-effective data layer for this requirement?

Answer options:

A.Azure SQL databases
B.Azure PostgreSQL
C.Azure Cosmos DB
D.Azure Data Lake

Answer - D 
And then, you can replace the answer text with the following. 
If you are looking at storing data that is not frequently used, you can use the Azure Data Lake service. 
The Microsoft documentation mentions the following. 

You should use Azure SQL, Azure PostgreSQL, or Cosmos DB for frequently accessed data. 
For more detailed information related to the pricing of Azure Data Lake Storage, please visit the following URL- 

https://docs.microsoft.com/en-us/power-bi/service-dataflows-connect-azure-data-lake-storage-gen2