The picture shows a flat shape with four equal sides and four right-angled corners.<br><br>
&bull; A circle is round &rarr; no.<br>
&bull; A rectangle has opposite sides equal, not necessarily all four.<br>
&bull; A triangle has only 3 sides &rarr; no.<br>
&bull; A square has 4 equal sides and 4 corners the same. &#10003;<br><br>
The shape matches all the properties of a square.<br><br>
Final Answer: D: square