The principle encourages us to resolve a set of stimuli, such as trees across a ridgeline, into smoothly flowing patterns

If this question has the same set of options as to the following, the answer would be letter d. Continuity.
Continuity in Psychology accounts for visual perception of immediate environments that piece together a background's individual elements to form a panoramic image. 

The choices are:
A.) depth perception. 
B.) perception. 
C.) similarity. 
D.) continuity.