B . True. Oracle databases guarantee read consistency at the transaction level, meaning that each query can only see data that has been committed before the query began executing.
C . True. When an UPDATE statement is executed, Oracle locks each row as it is updated to prevent other transactions from modifying it until the transaction is committed or rolled back.
A is incorrect because updates made by one user cannot be rolled back by another user. D is incorrect because a query can access tables in other schemas if proper permissions are granted. E is incorrect because a user can own only one schema, which has the same name as the user in an Oracle database.