Answer:
If you are in the same chem textbook as I am, (Chemistry, Connections to Our Changing World, from 1997) then the answer can be found on pg. 195, a page before the aforementioned question. If you aren't using this textbook, here's a summery of what it says: Magnesium and aluminum can be combined to form an alloy, which is used in things like car wheels, aircraft, tools, and furniture. It doesn't react with cold water, but it does react with hot water or steam. Calcium carbonate is found in chalk, marble, and limestone.