What should you do?

A SharePoint 2010 environment contains a Microsoft SQL Server 2008 R2 database instance named SP-SQL that hosts the databases for the farm.
You are upgrading the farm to SharePoint 2013.
You need to ensure that users can access the unmodified farm contents during the upgrade process.
What should you do?
A. In SQL Server Management Studio, locate the SQL Server instance containing the content databases and service application databases you plan to upgrade. Set the Instance Read-Only value to True.
B. In SQL Server Management Studio, locate the content databases and service application databases you plan to upgrade. Set the Database Read-Only value to True.
C. Run the following Transact-SQL (T-SQL) statement for each content database and service application you plan to upgrade. EXEC sp_dboption, “read only”, “True”;
D. Run the following command-line tool for each site collection in the content databases you plan to upgrade. Stsadm -o setsitelock -urlsite collection name> -lock readonly