Final answer:
In an experiment comparing hours of exercise to changes in blood pressure, the type of exercise would be a controlled variable to ensure consistent results.
Step-by-step explanation:
In the experiment to evaluate how the number of hours spent exercising each week affects blood pressure, the controlled variables are those that the experimenter keeps constant to ensure that any changes in blood pressure can be attributed to the exercise regimen. The variable that is intentionally changed is the number of hours spent exercising, which is the independent variable. In this experiment, c) Type of exercise would likely be a controlled variable, as different types of exercise may have varying impacts on blood pressure. These include intensity, duration, and the form of exercise. The blood pressure is the dependent variable as it is the outcome being measured, and it is expected to change in response to the exercise. The controlled variables are crucial for reducing confounding variables and for improving the reliability of the experiment's results.