Columnstore tables and indexes are always stored with columnstore compression. You can further reduce the size of columnstore data by configuring an additional compression called archival compression.
Note: Columnstore - The columnstore index is also logically organized as a table with rows and columns, but the data is physically stored in a column-wise data format.
Incorrect Answers:
B: Rowstore - The rowstore index is the traditional style that has been around since the initial release of SQL Server.
For rowstore tables and indexes, use the data compression feature to help reduce the size of the database.
Reference:
https://docs.microsoft.com/en-us/sql/relational-databases/data-compression/data-compression