Roberto noticed a lot of erosion on one hillside following a heavy rain . he wonders why one hillside shows more erosion than others. he sets up the experiment shows below .using a watering can to simulate rain , roberto pours the same amount of wáter at the same speed on each tray. identify the controlled variables and the variable that is tested in roberto's experiment .

a]soil 30° b]soil and gravel 30° c]soil and grass 30°

On simulating Rain Over three types of Terrain that  is Roberto is experimenting on shows the following result:-

a. Soil at 30 degrees- when water flows from inclined plane made up of soil, the water with it take the soil as there is nothing to stop erosion takes place at a faster in such terrains.

b. Soil and gravel at 30°-  when water flows from the inclination which has soil and gravel, both at the same time depicts a situation where land has already eroded. Hence it will have less amount of soil getting washed away.

c. Soil and grass at 30 degrees- In this experiment when water flows from the inclination the least amount of erosion for soil washing, takes place in this case. Because the grass roots are holding onto the soil and preventing erosion.