In the diagram, AC=BD. Show that AB=CD

I believe you just have to draw 2 little lines in between AB and CD.

Gravity is a force of attraction that brings all things (including terrestrial bodies) with mass towards one another. This brings, the sun, the planets and their moons together in orbit. On earth the gravity brings all things with mass towards the center of the earth. This explains the reason why all things thrown up falls back down.