The BA should create a process model to address the business sponsor's interest in improving a specific process that is in scope. This is because a process model is a visual representation of how a process works, including its inputs, outputs, activities, roles, events, rules, etc. Creating a process model can help to analyze and improve a process by identifying its current state, problems, gaps, opportunities, and desired future state.
The other options are not as relevant or helpful as creating a process model. References:
BABOK Guide, section 10.25: Process Modeling
CCBA Practice Test, question 111