Aisha wonders whether wind or water causes the most erosion. she set up an experiment in which she used a watering can to pour water down a pile of dirt. she then used a fan to blow wind on a second pile of dirt that is the exact same shape and size as the first pile of dirt. aisha then measured how the height of the dirt piles changed. she also drew pictures of how their shape changed. in this experiment, what was the dependent variable?