A large rock is motionless on a flat sidewalk. Which statement best explains why the rock remains motionless? A: The sidewalk exerts an unbalanced force on the rock.
B:The only force acting on the rock is directed toward the sidewalk.
C:The forces acting on the rock are all balanced.
D:There are no forces acting on the rock

The answer is D

Explanation:

there is no force on the rock

the total distance that martina travels that day is

(distance from home to mom's office) plus (distance from mom's office to school)

plus (distance from school to library) plus (distance from library to friend's house)

plus (distance from friend's house to martina's house).

(we don't know what any of these distance actually is.)