Sue wants to know whether wearing sunglasses improves driving performance. If she uses an independent groups design, she would manipulate the variable by randomly requiring half the drivers to drive with sunglasses and the other half to drive without sunglasses. having all drivers first drive without sunglasses and then with sunglasses. having half the drivers first drive without sunglasses and then with sunglasses and having the other half first drive with sunglasses and then without sunglasses. requiring all drivers to first drive with sunglasses and then without sunglasses.