سوال ۲۱ کنکور ارشد علوم کامپیوتر ۱۳۹۷

PASSAGE 2 (excerpt):

"In three-dimensional computer graphics, fractal techniques have been used to generate terrain models and the easiest techniques involve subdividing the faces of the objects that consist of triangles or quadrilaterals. A recursive subdivision procedure is applied to each facet, to a required depth or level of detail, and a convincing terrain model results. Subdivision in this context means taking the midpoint along the edge between two vertices and perturbing it along a line normal to the edge. The result of this is to sub-divide the original faces into a large number of smaller facets, each having a random orientation in three-dimensional space about the original facet orientation. The initial global shape of the object is retained to an extent that depends on the perturbation at the subdivision and a planar four-sided pyramid might turn into a 'Mont Blanc' shaped object."

21. With the use of subdivision, ----------.