They need an independent variable, in this case it should have been the fish food. Everything should be identical except the fish food, from what I read , it doesn't say anything about what type of food they used, or the dosage.
The correct option is deposition.
Deposition is the process by which sediments, soils and rocks are added to a particular rock which result in successive layers in the rock. Deposition is usually brought about by the action of wind, water, ice and gravity. These forces brings on sediments which are added to the rock layers.
The answer should be all of the above, if it is not then the answer is A dichotomous key can help classify an unknown organism.
Hope this helps, if not, comment below please!!!!
