Which of the following human activities would be most beneficial to soil conservation?

The best answer is D because construction would be bad for the environment and take up space on the soil that is trying to be preserved. Also, for C, planting only one crop type in soil is not very beneficial to the soil at all. IT is best to plant multiple crops in the soil and move the crops to different parts of the soil each year when planting them. 

It depends on the surface of the levels. the rougher the surface, the greater is the frictional force. for rougher surfaces, you would need to exert greater force to move the object. the concept is that, you must overcome the frictional force in order to bring the object into motion. this is the reason why we add lubricants to the joints so they could easily move. this answer was on