Question

Based on investigations with the horse Clever Hans, an important factor researchers should seek to control when testing whether dogs can sniff cancer in urine samples is
A. whether the dogs are tested indoors or outdoors.
B. that some samples should come from people and some from horses.
C. that the urine samples should come from a diverse group of patients.
D. whether, during testing, the dogs can see people who know which samples came from cancer patients.

Answer

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