Surface Generation — A ruled surface can be generated by moving a straight generatrix along one or more directing curves (the path), producing a surface traced by straight-line elements.

Introduction / Context:
Ruled surfaces are foundational in geometry and fabrication: a straight line (the generatrix) sweeps along a guide path to create a surface that contains straight-line elements. Classic examples include cylinders, cones, and hyperbolic paraboloids.

Given Data / Assumptions:

• The generatrix is straight at all times.
• One or more directing curves constrain the motion.
• The resulting surface contains a straight-line element through every point.

Concept / Approach:
Because the surface is traced by straight lines, it inherits useful properties for construction and analysis. Many ruled surfaces are also developable (e.g., cylinder, cone), which simplifies pattern creation and forming.

Step-by-Step Solution:
1) Choose the directing curve(s) (e.g., axis line, rim curve).2) Move a straight line so that it remains in contact with the curve(s).3) The envelope of the line’s positions forms the ruled surface.4) Extract edges and true lengths for fabrication or modeling.

Verification / Alternative check:
Sampling points on the surface reveals a straight ruling through each point, confirming the ruled nature.

Why Other Options Are Wrong:
A circular generatrix would not be a straight-line ruling; perspective is unrelated to definition; cylinders and cones are examples, not the only cases.

Common Pitfalls:
Confusing ruled with merely “swept” surfaces that use curved profiles; assuming all ruled surfaces are developable (not all are).

Final Answer:
Correct