How many quadrilaterals in the diagram. (Diagram [20].)
Why is Fig. a d a quadrilateral?
What is a quadrilateral?
On account of the number of its angles, what may it be called?
Name all the quadrilaterals.
Name three trapeziums.
Why is Fig. 5 a trapezium?
What is a trapezium?
Name two trapezoids.
Why is Fig. 6 a trapezoid?