Thank you for the opportunity to help you with your question!
The answer is B: "in the wild studies". There is a good book on this subject called Interaction Design: Beyond Human-Computer Interaction by Jenny Preece, Helen Sharp, and Yvonne Rodgers. Page 455 in this book will give you the same answer.
Please let me know if you need any clarification. I'm always happy to answer your questions.
Jun 21st, 2015
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