Final answer:
The correct answer is b. relative; period. NNT, which stands for Number Needed to Treat, is a measure used in medical research to evaluate the effectiveness of a treatment.
Step-by-step explanation:
The correct answer is b. relative; period. NNT, which stands for Number Needed to Treat, is a measure used in medical research to evaluate the effectiveness of a treatment. When calculating the NNT, it is important to consider the time period during which the effects of the treatment were observed, which is why the correct answer includes the term 'period'.