What type of data source is used in a SAS DATA step?

The correct choice is that all types of data from various programs can be used in a SAS DATA step. A SAS DATA step is designed to handle diverse data sources, including but not limited to SAS datasets, external files (like CSV or Excel), and data generated from other SAS procedures or programs. This flexibility allows SAS to assimilate, manipulate, and analyze data from various origins seamlessly.

This capacity to work with multiple data types enhances the versatility of SAS programming, as it can directly read and process information from different formats, making it a favored choice for data preparation and management. This feature is particularly useful in data integration tasks where data from disparate sources needs to be combined or transformed for analysis.

The other options are limited in scope. For instance, stating that only external files or exclusively manually entered data can be used overlooks the capabilities of the DATA step to work with a matrix of data sources. Similarly, asserting that it can only handle SAS datasets created from scratch ignores the capacity to read pre-existing datasets as well.