Answer:
B. Gravitational force
Explanation:
The gravitational force of an object (also called weight) is given by
[tex]F=mg[/tex]
where m is the mass of the object and g is the acceleration of gravity, and it always points in the downward direction.
In this problem, the arrow labelled with 4 is the only force pointing downward: therefore, it must be the gravitational force.
The other arrows represent:
1 --> component of the gravitational force parallel to the plane
2 --> force of friction
3 --> component of the gravitational force perpendicular to the plane
