Geometry

Question Analysis:
This question involves verifying a claim using properties of regular polygons and exterior angle relationships.
The main focus is on understanding how the measure of an exterior angle determines the number of sides, only in regular polygons.

Key Concept Explanation:
For regular polygons, each exterior angle = 360° ÷ n
If given one exterior angle (20°), then: n = 360 ÷ 20 = 18 sides
However, in irregular polygons, not all angles are equal — so 20° could be just one of several angles and doesn't uniquely determine the number of sides.

Step-by-Step Solution:
Assume regular polygon → exterior angle = 20°
⇒ n = 360 ÷ 20 = 18 sides
But the student's claim doesn't mention "regular" — which is important
In an irregular polygon, one exterior angle may be 20°, but others could be different.
So: ✅ The claim is only correct if the polygon is regular

Option Analysis:
A. ❌ Too strong – applies only to regular polygons
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