Changing the default configurations of a database system is a critical control for securing it from unauthorized access or exploitation. Default configurations often include weak passwords, unnecessary services, open ports, or known vulnerabilities that can be easily exploited by attackers. The other options are not as important as changing the default configurations, as they do not address the root cause of the security risks. Normalizing tables in the database is a design technique for improving data quality and performance, but it does not affect security. Changing the service port used by the database server is a form of security by obscurity, which can be easily bypassed by port scanning tools. Using the default administration account after changing the account password is still risky, as the account name may be known or guessed by attackers. References: CISA Review Manual (Digital Version), Chapter 5, Section 5.2.4