The factor that influences the mass movement of particles is large rocks and debris on a slope.
Mass movement, or mass wasting, refers to the downward movement of soil and rock material under the influence of gravity. Large rocks and debris on a slope can contribute to instability and increase the likelihood of mass movement, such as landslides or rockfalls. Other factors can also play a role, but among the options provided, this one is the most directly related to mass movement.