Your application needs sub-millisecond latency for cached data. What GCP service should you use?

Correct answer: Memorystore (Redis/Memcached)

Option B is correct because Google Cloud Memorystore is a fully managed in-memory data store service supporting Redis and Memcached, both of which deliver sub-millisecond read and write latency by keeping data entirely in RAM. Option A is incorrect because Cloud Storage is an object store designed for durability and large-scale data retrieval, with latencies measured in tens to hundreds of milliseconds, far above the sub-millisecond threshold. Option C is incorrect because Cloud Firestore is a serverless document database optimized for mobile and web apps, offering single-digit millisecond latency at best, not sub-millisecond. Option D is incorrect because Cloud SQL is a relational database backed by persistent disk, and while it can be fast, it cannot consistently achieve sub-millisecond latency for cached data the way an in-memory store can.