Exercise 2: sample answer

Hub gears are sealed inside the rear hub, so they are protected from weather and dirt, can be changed while stopped, need little maintenance and suit commuting and town bikes. Derailleurs move the chain between sprockets of different sizes, giving many gears, a lighter and more efficient system, and a wide range, which suits racing, touring and hill riding, though the exposed parts need cleaning and adjusting. Hub gears are better for low maintenance; derailleurs for range and weight (check typical numbers of gears).