Final answer:
A well-defined, testable question in a science investigation is clearly stated, can be tested in an experiment, and the results can be measured. (option c)
Step-by-step explanation:
In a science investigation, a well-defined, testable question is one that is clearly stated and can be tested in an experiment, with results that can be measured. It is important that the question is clearly defined and that it can be tested using the scientific method. For example, a well-defined, testable question in a biology investigation could be: 'Does the amount of sunlight affect the growth of plants?'