The correct answer is A flexible schema that allows frequent and easy restructuring of table rows.

Relational databases define a fixed schema made of tables and columns and they expect schema changes to be explicit operations such as ALTER TABLE. Because of that they are not designed for frequent and easy restructuring of table rows and that is why the bolded option is not a typical characteristic of a relational database.

Data integrity enforced through primary foreign and check constraints is a hallmark of relational systems. Primary keys foreign keys and check constraints are used to maintain data integrity so this option is typical of relational databases and therefore not the correct answer.

Cloud Spanner is a managed relational database offering that supports relational schema and SQL features. As a relational product it does not represent an atypical characteristic and so it is not the correct choice.

Atomicity consistency isolation and durability guarantees for transactions describe the ACID properties that relational databases commonly provide. Because transactional ACID guarantees are typical of relational systems this option is not the correct answer.

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