Two sides with a common end point are consecutive sides.

(a)  

The word "quadrilateral" is composed of two main parts: "quad" which means "four" and which means "side"

(a)  

The diagonals of a rectangle are congruent.

(a)  

The diagonals of a square are congruent.

(a)  

The diagonals of a square are perpendicular bisectors to each other.

(a)  

Each diagonal of a square bisects a pair of opposite angles.

(a)  

The diagonals of a rhombus are perpendicular bisectors to each other

(a)  

Each diagonal of a rhombus bisects a pair of opposite angles.

(a)  

In the proof of "The diagonals of a rectangle are congruent", given with a rectangle ABCD, the reason for $$AD\ \cong\ BC$$  is that the opposite sides of a parallelogram are congruent.

(a)  

A parallelogram is a type of quadrilateral whose pairs of opposite sides are parallel.

(a)  

If a quadrilateral is a rhombus, then it is a parallelogram

(a)  

If one pair of a consecutive sides are congruent, then a parallelogram is a rhombus

(a)  

If a quadrilateral is a rectangle, then it is a parallelogram.

(a)  

If a parallelogram is a rectangle, then its diagonals are congruent.

(a)  

A square is a quadrilateral with four right angles and four congruent sides.

(a)  

All squares are rectangles

(a)  

If one angle is a right angle, then a parallelogram is a rectangle

(a)  

If one diagonal bisects a pair of opposite angles, then a parallelogram is a rhombus.

(a)  

Opposite angels refers to two angles whose vertices are not endpoints of the same side.

(a)