The correct answer is: Allows flexible schemas so data can be stored as key value pairs documents or graph models.

This option is correct because nonrelational databases are designed to accept semi structured and evolving data without a fixed table layout. Flexible schemas let you store different records with different fields and nested structures which makes it easier to model documents key value pairs or graphs and to iterate on the data model as requirements change.

Choosing a nonrelational store gives you schema flexibility and horizontal scalability which helps when you need to ingest varied or rapidly changing data. Those benefits come with trade offs that you should evaluate but they align directly with the startup use case that wants to hold semi structured documents and graphs.

Enforces referential integrity with foreign key constraints across tables is incorrect because referential integrity and foreign keys are features typically provided by relational databases. Many NoSQL systems do not enforce foreign key constraints automatically and expect the application to manage those relationships.

Cloud Bigtable is incorrect because it names a specific GCP product rather than stating a general benefit. Cloud Bigtable is a wide column key value store that is optimized for large scale time series and analytical workloads and it is not primarily a document or graph database.

Provides strong multi row ACID transactions by default is incorrect because most nonrelational databases do not offer strong multi row ACID transactions by default. Strong multi row ACID guarantees are more commonly associated with traditional relational systems or specialized distributed databases that are designed to provide both scale and transactional semantics.

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