Final answer:
Dr. Hernandez can classify the specimen as living by observing its functions, which include metabolism, growth, reproduction and response to stimuli, as these are characteristics of living cells.
Step-by-step explanation:
Dr. Hernandez can correctly classify the microscopic single-celled specimen as a living specimen by observing what functions the specimen is able to perform. This direct observation of functions like metabolism, growth, reproduction, and response to stimuli is critical because all living organisms display these characteristics. Simply determining whether the specimen has organelles (Item A) or not might not sufficiently prove it is living, as some living cells are prokaryotic and do not have membrane-bound organelles.
Chemical treatment reactions (Item C) might not be conclusive, as some non-living things can also react chemically. Replication (Item D) is important for life but observing it alone could miss other vital functions. Therefore, it is essential that these functions are confirmed under controlled experimental conditions. Studying the specimen's behavior through a microscope, as Antonie van Leeuwenhoek did with the first observed living cells, would be a practical approach to determine its living status.