A: Incorrect. An uncommitted transaction is not automatically committed if the user exits SQL*Plus. It is rolled back unless otherwise specified. B. Correct. A DML statement such as INSERT, UPDATE, or DELETE will implicitly start a new transaction if there is no current transaction running in the session. C. Incorrect. A user cannot see uncommitted updates made by another session; a session can only see its own uncommitted changes. D. Incorrect. A Data Definition Language (DDL) statement automatically commits any outstanding transactions in the session, not just the changes to the data dictionary. E. Correct. A session can always see its own uncommitted updates. This is because Oracle uses a multiversion consistency model, allowing each user to see a consistent view of the data including their own changes. F. Incorrect but close. If a session has an uncommitted transaction, then a DDL statement does issue a COMMIT before executing and starting a new implicit transaction, not just for the data dictionary updates but for all pending changes in the session.
This information can be verified in the Oracle Database SQL Language Reference and Oracle Database Concepts documentation, which discuss transaction management and the behavior of DML and DDL statements within transactions.