Your choices for materials to compare in this worksheet are:
granite and marble
copper and aluminum
bituminous coal and anthracite
You may NOT use Aluminum and Tin, as they are used in the examples.
If you want to compare a different set of rocks or minerals, feel free. Just make sure they are both used for the same purpose. The point of the lab is to compare the two rocks/minerals and decide which one is better for that specific purpose.