Geometry

Question Analysis
This question examines essential properties of right circular cones.
The main focus is distinguishing necessary vs. accidental features.

Key Concept Explanation
Right circular cone definition:
Circular base (must be perfect circle)
Apex perpendicular to base center (not edge)
Single circular face (no parallel faces)
Slant height: Diagonal distance (generally ≠ radius)

Step-by-Step Solution
Eliminate A: Apex must be above center, not edge.
Eliminate B: l =

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