Which of the following is not an assumption that is critical to the scientific method

The answer would be D. Empiricality. Scientific Method can not, and will not deal with studies that are either for logic or for theism. This field may be beyond the scientific confirmability, meaning, it can not be proven by science, one example of this is the existence of a primary mover, or a God.

The rock found in the riverbed that is smooth is from the result of weathering of water in the river and erosion. The rock deep underground was most likely a product of erosion. The dirt and ground above it were eroded and displaced there to cover the rock.