Answer:
Perspective and color
Step-by-step explanation:
The two techniques that help in creating an illusion of depth on a flat surface are perspective and color.
Perspective can be defined as an art of creating three-dimensional objects on a two-dimensional surface. This technique in drawing helps to create a realistic painting on a piece of paper or canvas (two-dimensional). It helps in creating an illusion of space and depth in a painting or drawing.
Color is the other technique used to create an illusion of depth on a flat surface. Depth can be created depending upon the color of the background. Cool colors such as blue, green, etc will appear farther and warm colors such as red, yellow, orange, closer on a black background. On the other hand, on white background, cool colors appear near and warm colors farther.
So, the correct answer is perspective and color.