You are migrating a database named Orders to a new server that runs Microsoft SQL Server 2012.
You attempt to add a SQL login, [User1], to the database. However, you receive the following error
message:
“User already exists in current database.”
You need to configure the [User1] login to be able to access the Orders database and retain the
original permissions. You need to achieve this goal by using the minimum required permissions.
Which Transact-SQL statement should you use?

A.
DROP USER [User1];
CREATE USER [User1]FOR LOGIN [User1]; ALTER ROLE [db_owner] ADD MEMBER [User1];

B.
ALTER ROLE ;db_owner] ADD MEMBER [User1];

C.
ALTER USER [User1]WITH LOGIN [User1];

D.
ALTER SERVER ROLE [sysadmin] ADD MEM3ER [User1];

Explanation:
Reference:
http://msdn.microsoft.com/en-us/library/ms176060.aspx