Identify criteria to establish causality.

Thirty minutes of exercise per day can reduce your blood pressure.

Which of the following is a guideline for establishing causality?

• a.) Control the number of minutes of exercise and blood pressure to get the same results.
• b.) Check if lower blood pressure is present or absent when exercise is present or absent.
• c.) Look for evidence that smaller amounts of exercise produces a reduction in blood pressure.
• d.) Perform a randomized, controlled experiment.