Answer:
It helps distinguish elements in a layout. Contrast
It is a system of organization that organizes things according to their relative importance. Hierarchy
It provides a strong sense of belonging of elements, creating a whole. Repetition
It provides details and interest for the eye. Imperfection
Explanation:
Contrast is basically how different elements are in a design, specially adjacent elements. These differences make the elements stand out. Lack of contrast can make text content difficult to read for example, so it's very useful to distinguish elements in a layout.
Hierarchy, in design, relates to the importance of elements within a design. It is the control of the visual information in a design to imply importance.
Repetition, in design is a great way to unify a design that brings a lot of different elements together. Repetition of design elements will bring a clear sense of unity, consistency and cohesiveness. It can be done by repeating the same color, typefaces, shapes, or other elements of a design.
Imperfection, in design, consists on accepting and finding beauty in imperfection, using concepts as asymmetry, roughness, simplicity, economy, austerity, which in turn, make the designs striking to the eye.