Final answer:
The variables in a research study must be clearly defined or operationalized to be replicable; the correct term is 'Precise'. Operationalization is crucial for consistency and validity in studies.
Step-by-step explanation:
To conduct research that is replicable, the variables must be clearly defined in specific terms, or operationalized. The correct answer is a) Precise. This is important in research as it ensures other researchers can collect data in a systematic and replicable manner. According to the operational definitions, set a represents a precise, but inaccurate set of measurements, set b represents a set of measurements that is both precise and accurate, and set d represents a set of measurements that is neither precise nor accurate. Additionally, for a measurement to be considered valid in the context of the topic of study, it is important that the study measures what it is designed to measure and follows appropriate steps to ensure objectivity.