The correct answer is C because Pub/Sub is ideal for ingesting data from IoT devices, offering a globally durable message ingestion service that can handle spikes in data volume. Bigtable is well-suited for storing time series data, providing low-latency and high-throughput for NoSQL data, making it perfect for scenarios where data needs to be quickly accessible for visualizations and queries.

• Option A is incorrect because Dataproc is not designed for data ingestion in IoT solutions and Datastore is not optimized for time series data storage.
• Option B is incorrect because Dataproc is not an ideal service for data ingestion in this context, despite Bigtable being suitable for storage.
• Option D is incorrect because Datastore is not the best choice for storing time series IoT data, even though Pub/Sub is correct for ingestion.

For more details, refer to the GCP documentation on IoT Overview.