The correct choice is Define a local secondary index when creating the table. A local secondary index preserves the same partition key and provides an alternate sort key and it must be declared at table creation to satisfy the requirement.

An LSI shares the table partition key and lets you query items with a different sort key without changing the partitioning of the data. An LSI must be created with the base table so you cannot add it later and that constraint matches the question exactly.

Run a Scan operation is incorrect because scanning reads every item in the table and it does not provide any indexing or efficient targeted queries.

Create a global secondary index is incorrect because a global secondary index can be added after table creation and it often uses a different partition key, so it does not enforce the same-partition-key plus alternate sort-key requirement at creation time.

Enable DynamoDB Streams is incorrect because streams capture change events for replication and processing and they do not create or change query indexes or sort keys.

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