Decide whether the syllogism represents correct or flawed reasoning. If flawed, explain why the conclusion is not a valid.

1. All triangles are polygons.
Figure ABC is a triangle
Therefore, figure ABC is a polygon.

2. No trapezoids are rectangles.
Some rectangles are not squares.
Therefore, some squares are not trapezoids.

3. If polygon ABCD is a square, then it is a rectangle.
Polygon ABCD is a rectangle.
Therefore, polygon ABCD is a square.

4. If polygon ABCd is a square, then it is a rectangle.
Polygon ABCD is not a square.
Therefore, polygon ABCD is not a rectangle.