Final answer:
Workflow Foundation allows a mix of composition language and programming language in a workflow development environment, providing a versatile platform within the .NET framework for workflow-enabled applications.
Step-by-step explanation:
The workflow development environment that allows the mixing of composition language and programming language is Workflow Foundation (also known as WF). Workflow Foundation is part of Microsoft's .NET framework and provides a robust platform for building workflow-enabled applications.
It integrates a variety of programming languages through the .NET framework, and its activities can be extended with custom code, marrying composition and programming within the same environment.
Other options like Oracle BPEL and Oracle BPM Suite are more focused on business process management and enterprise-level integration, typically using standardized composition languages like BPEL, whereas Kepler workflow system is designed primarily for scientific workflows and may not offer the same flexibility in integrating programming languages as WF does.