Which form mainly has flat planes and sharp edges?

Cube

The governing concept is the distinction between geometric solid forms. A cube is a solid with six flat square faces, straight edges, and sharp or clearly defined corners. Therefore, option A is correct: its planes and edges are the main visual features that describe its form. A sphere, option B, has one continuously curved surface and no straight edges or corners. Smoke, option C, is generally an irregular, changing substance rather than a stable geometric solid with fixed planes. A cloud, option D, may have soft, irregular, rounded contours and does not mainly consist of sharp planar faces. When drawing a cube, artists often use straight construction lines, perspective, and value changes across separate planes to show its volume. These differences help distinguish angular forms from rounded or irregular forms.

This is a Class 9 Art Education question. Chapter: Elements of Art. Topic: Form.