Students in a college made this hypothesis: ‘reaction time will increase as the time you have been awake increases.’ The students set up an investigation to test their hypothesis. This is the method used. 1. Find 5 volunteers willing to stay awake for 24 hours. 2. Keep the volunteers in a room where they can study, use an exercise bike or watch TV as they wish. 3. Provide food, water, coffee and tea as requested. 4. Measure the volunteers’ reaction time every 4 hours using a computer program. (b) What was the independent variable in this investigation? _______________________________________________