Centralize various on-prem and cloud unstructured files (Parquet, CSV) into Cloud Storage using a GUI-based tool and support using customer-managed encryption keys for the object sink.

Cloud Data Fusion is the correct choice because it is a fully managed, cloud-native data integration service built on open-source CDAP, offering a graphical user interface (GUI) for building and managing ETL/ELT pipelines. This directly addresses the requirement for a GUI-based tool to centralize unstructured files. It also supports customer-managed encryption keys (CMEK) for Cloud Storage sinks, fulfilling the encryption requirement. BigQuery Data Transfer Service is incorrect because it is designed for transferring data into BigQuery, not for centralizing unstructured files in Cloud Storage, and it doesn't offer a general-purpose GUI for file transfers. Storage Transfer Service can move files to Cloud Storage but lacks the GUI-based pipeline development and robust transformation capabilities of Data Fusion. Dataflow is a powerful processing engine but requires coding (Java, Python, SQL) to define pipelines, which contradicts the GUI-based tool requirement.