Explanation/Reference:
Explanation:
UserA: db_accessadmin
Members of the db_accessadmin fixed database role can add or remove access for Windows logins, Windows groups, and SQL Server logins.
UserB: db_datareader, db_datawriter
Members of the db_datareader fixed database role can run a SELECT statement against any table or view in the database.
Members of the db_datawriter fixed database role can add, delete, or change data in all user tables.
UserC: db_ddladmin
Members of the db_ddladmin fixed database role can run any Data Definition Language (DDL) command in a database.
Incorrect Answers:
Not db_owner
Members of the db_owner fixed database role can perform all configuration and maintenance activities on the database.
References:
https://technet.microsoft.com/en-us/library/ms191451(v=sql.90).aspx
https://technet.microsoft.com/en-us/library/ms190667(v=sql.90).aspx