Final answer:
Dr. Tierno's answer to the question about pillows involved testing them for microorganisms to investigate hygiene-related issues, distinguishing his method from surveys, sleep pattern analyses, or expert interviews.
Step-by-step explanation:
Dr. Tierno found an answer to his question about pillows by c) testing pillows for microorganisms. This approach involved examining the cleanliness of pillows and determining the presence of potentially harmful organisms. Unlike the other options, which include conducting surveys, analyzing sleep patterns, or interviewing experts, Dr. Tierno's methodology was more laboratory-based and focused on the biological aspects implicated in hygiene and health, particularly as they relate to sleep hygiene.