Which of the following four items are considered primary factors in natural selection? A) struggle for existence
B) gene pool
C) adaptation
D) descent with modification
E) genetic drift
F) the heritable genetic variation of individuals
G) mass extinction events
H) geological events, such as volcanic eruptions and earthquakes

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