A polygon is a closed figure made by joining line segments, where each line segment intersect exactry two other line segments.
A polygon is said to be a regular polygon if the sides are all of the same length.
Thus, the figures that are polygon are:
Figure A which has 6 sides all made of line segments.
Figure B which is a regular hexagon, having 6 sides made all of segments.
Figure D has 7 sides which are all segments.