Geometry

Question Analysis:
This is a concept-based multiple-select question focusing on essential features of pyramids.
The main focus is on recognizing structural requirements.

Key Concept Explanation:
Pyramids have:
One polygonal base
Triangular sides
One common apex
All side surfaces must be flat, not curved

Step-by-Step Solution:
A: ✅ Yes, pyramids only have one base
B: ✅ Yes, must be a polygon (not a circle)
C: ❌ Curved sides → cone
D: ✅ Triangular sides are required...