c. Parallel lines are taken to parallel lines.

In The Polar Express, there's a scene at the North Pole in which five or six different sets of train tracks all come out a hub, like spokes on a bicycle. The train spins round and round, and finally ends up on one particular set of tracks.

What if, instead, the hub stayed steady and the tracks spun? Probably not the most ideal mode of public transport, but it would be a great example of parallel lines being transformed by a rotation.

Students should know that when we're talking about transforming parallel lines, we're treating both lines as part of the same image. Whatever we do to one, we'll do to the other. So naturally, it makes sense that the two lines will stay parallel to each other no matter which of those three transformations we perform.

Students should also understand that not all lines have to be straight in order to be parallel. They can think of train tracks going around a mountain, curving as they go. As long as they have the same slope at any given point, they'll be parallel.