Which line is useful to show the flow of a river simply?

Correct answer: Wavy line

The direct answer is D, Wavy line. In visual art, line direction and shape can suggest movement. A river usually bends and its surface has repeated wave-like movement, so a wavy line communicates flowing water simply. Step by step: identify the subject as moving water; choose a line that bends rhythmically; the repeated curves suggest flow; therefore option D is best. Option A, broken line, shows interruption or separate marks and is less suitable for continuous flow. Option B, straight line, can show a rigid edge, horizon or direction, but it does not naturally suggest a winding river. Option C, thick line, describes width or weight, not the kind of movement. Option D is correct because its curves visually imitate waves and flowing water. This is a simple visual symbol, not a rule that every river must be drawn only this way. Memory cue: flowing water—think waves, so choose a wavy line.