Angles on parallel lines
Change the slope of the vertical line and describe what relationships you see between the angles.
Are some angles equal? Do some add up to 180 degrees? Think of the letters Z, C, F, can you link these to the angles you've found? Look up the definitions for vertically opposite angles, corresponding angles, alternate angles, supplementary angles. Can you relate these definitions to the angle relationships you've already found? Now make a poster to demonstrate what you have discovered, use diagrams as well as definitions.