https://docs.snowflake.com/en/user-guide/warehouses-multicluster.html#:~:text=Auto%2Dscale,-You%20can%20choose&text=This%20mode%20is%20enabled%20by,while%20the%20warehouse%20is%20running.

For variable compute needs, auto scaling should be used

multi cluster for concurrency

I think A

D is correct answer

In Auto-scale mode, a multi-cluster warehouse eliminates the need for resizing the warehouse or starting and stopping additional warehouses to handle fluctuating workloads. Snowflake automatically starts and stops additional clusters as needed.

D. When a large number of concurrent queries are run on the same warehouse

correct

Auto-scale This mode is enabled by specifying different values for maximum and minimum number of clusters. In this mode, Snowflake starts and stops clusters as needed to dynamically manage the load on the warehouse: As the number of concurrent user sessions and/or queries for the warehouse increases, and queries start to queue due to insufficient resources, Snowflake automatically starts additional clusters, up to the maximum number defined for the warehouse. Similarly, as the load on the warehouse decreases, Snowflake automatically shuts down clusters to reduce the number of running clusters and, correspondingly, the number of credits used by the warehouse.

It can't be A because SF recommends experimenting when you don't know the right size/number of clusters for your wh.