C

#Vortices, rotary movements, tornadoes #Waves, sound and micro waves. #More than two circles, inside one another, spirals #Rectangles #Quadrilaterals containing one or more other geometrical figures (specify the content) #Quadrilaterals with dark surfaces or parts of surfaces #Other combinations of different geometrical figures, juxtaposed, joined or intersecting, combinations of more than two different geometrical figures #Letters or numerals forming geometrical figures, written or typographical matter in perspective #Letters or numerals representing a human being or a part of the human body, an animal or a part of an animal's body, a plant, a heavenly body, a natural phenomenon or an object #Letters in light-coloured characters on a dark background