The correct answer is C because Pub/Sub is designed for efficient message ingestion, making it ideal for handling data from numerous IoT devices. Bigtable, on the other hand, excels at storing time series data due to its low-latency and high-throughput capabilities for NoSQL data. This combination ensures scalable ingestion and efficient storage of time series data.

• Option A is incorrect because Datastore is not optimized for time series data storage.
• Options B & D are incorrect because Dataproc, being a managed Hadoop and Spark service, is not suited for direct data ingestion in IoT solutions. Additionally, its HDFS-based storage is not ideal for time series data compared to Bigtable.