The artist primarily used to show depth and create emphasis in this painting

if its only one word i'd say Perspective.

The artist used the perspective to show depth and create emphasis in this painting.

Explanation:

The linear perspective system projects the illusion of depth on a two-dimensional plane by the use of “vanishing points” to which all lines converge at eye level on the horizon. In the case of this painting, the artist used a vanishing point formed by the horizon and a group of parallel lines that converge on the center of the canvas. Also, clouds behave in the same way, converging to the center, distorting its form.

correct answer is b "write as much as you can about the subject so you might earn extra-credit points"