which shape is regular?

Explanation:

Step1: Recall regular - shape definition

A regular shape has all sides equal and all angles equal.

Step2: Analyze green pentagon

The green pentagon appears to have all sides and angles equal, so it could be regular.

Step3: Analyze purple semi - circle

A semi - circle is not a polygon with equal sides and angles, so it is not regular.

Step4: Analyze red octagon

The red octagon appears to have all sides and angles equal, so it could be regular.

Step5: Analyze blue trapezoid

The blue trapezoid does not have all sides and angles equal, so it is not regular.

Answer:

The green pentagon and the red octagon are regular shapes.