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.