How can visual heat or warmth be suggested through line?

Correct answer: Rising wavy lines

The correct answer is A: rising, wavy lines can suggest hot air or heat moving upward. In art, some effects cannot be seen as solid objects, so artists use visual symbols and directional marks. Wavy lines rising from a flame, road, or hot surface can represent moving air and shimmer. Their upward movement and irregular flow make the viewer think of heat rising. Option A is correct because both its direction and waviness support this suggestion. Option B is wrong because calm horizontal lines usually communicate stillness or rest, not rising heat. Option C is wrong because square or angular marks alone do not clearly suggest warmth or upward movement. Option D is wrong because a thick closed boundary mainly shows an edge or enclosure; it does not show heat travelling through the air. These are artistic conventions rather than measurements of temperature, and context remains important. Memory cue: rising, wavering marks often suggest invisible movement such as heat or smoke.