Final answer:
The double-blind method is a system used for reducing bias and error in the measurement of data.
Step-by-step explanation:
The correct answer is D. the double-blind method.
The double-blind method is a system used for reducing bias and error in the measurement of data. It is commonly used in clinical research trials where information about the treatment a participant receives is not disclosed to either the patient or the researcher. This helps to minimize any potential bias that could arise from the knowledge of the treatment.