Your organization is developing an application that will capture a (Digital Leader)

Correct answer: D) Cloud Bigtable.
For the described scenario of capturing a large amount of data from millions of sensor devices worldwide, and the need for high-speed data storage of unstructured data, Cloud Bigtable would be a suitable choice.

Cloud Bigtable is a fully managed, highly scalable NoSQL database service designed for large analytical and operational workloads. It is well-suited for handling massive amounts of unstructured data with low-latency read and write operations. Cloud Bigtable is particularly useful for time-series data, IoT applications, and scenarios where high-throughput and low-latency access to large-scale data are essential.

Firestore (A) is also a NoSQL database, but Cloud Bigtable may be more suitable for large-scale, high-speed, and unstructured data scenarios. Cloud Data Fusion (B) is a data integration service, and Cloud SQL (C) is a fully managed relational database service, which may not be the optimal choice for unstructured data at the scale described in the scenario.