A physics class has decided to create hot air balloons made of tissue paper. Each group creates a balloon of the same size from the same materials but of different masses. The groups use the same size candle in each balloon and measure the maximum height ofthe balloon using geometry. Which variables must be kept constant during the experiment? Select one: Q a. materials, size of candle and height O b. materials, size of balloon and size of candle O c- materials, size of balloon and height Q d. materials, size of candle and mass of balloon