Which approach enhances the portability of a database-connected application?

The usage of Structured Query Language (SQL) enhances the portability of a database-connected application because SQL is a standardized language used for accessing and manipulating databases. Most relational databases support SQL, allowing applications developed with SQL to work across different database platforms with minimal modification. This widespread adoption makes it easier for developers to share and use applications across multiple systems without the need for extensive rewriting of the database interaction code.

In contrast, verification of database import/export procedures focuses on the specific methods for transferring data between systems, which can vary significantly across different environments and doesn't inherently contribute to portability. The analysis of stored procedures and triggers typically ties applications to a specific database's features, as stored procedures and triggers are often not compatible across different database systems. Synchronization of entity-relation models with physical schemas deals more with ensuring that the logical design aligns with the actual database layout, which is crucial for functionality but does not enhance the capability of the application to operate on different database platforms. Hence, while each option addresses important aspects of database management, SQL remains the most relevant for ensuring portability in database-connected applications.