Final answer:
The nurse asking if the client is having pain is the action that clearly demonstrates assessing, as it involves collecting data to understand the client's health status.
Step-by-step explanation:
The action that demonstrates assessing is C) the nurse asking if the client is having pain. Assessing is a fundamental part of the nursing process, which involves collecting data to understand the client's health status and needs. When the nurse observes the client grimacing and then inquires about pain, she is gathering vital information that will influence how to proceed with care. Documentation and making the client comfortable are also important but are subsequent steps following the initial assessment.