Jeopardy for the classroom

Shapes

1. A shape with four sides of equal length.
2. The shape of an egg and some race courses, such as the Indianapolis Motor Speedway, site of the Indianapolis 500.
3. A three-sided shape.
4. The shape of a blackboard or whiteboard, and also most computer screens.
5. The shape of the Earth and the moon, not to mention a basketball or baseball.